constsquare= n => n * n;
+constdouble= n => n *2;
+const fn =overArgs((x, y)=>[x, y], [square, double]);
+fn(9,3);// [81, 6]
+
pipeAsyncFunctions
Performs left-to-right function composition for asynchronous functions.
Use Array.reduce() with the spread operator (...) to perform left-to-right function composition using Promise.then(). The functions can return a combination of: simple values, Promise's, or they can be defined as async ones returning through await. All functions must be unary.
const sum =pipeAsyncFunctions(
+ x => x +1,
+ x =>newPromise(resolve =>setTimeout(()=>resolve(x +2),1000)),
+ x => x +3,
+ async x =>(await x)+4
+);
+(async()=>{
+ console.log(awaitsum(5));// 15 (after one second)
+})();
+
pipeFunctions
Performs left-to-right function composition.
Use Array.reduce() with the spread operator (...) to perform left-to-right function composition. The first (leftmost) function can accept one or more arguments; the remaining functions must be unary.
Creates a function that invokes the provided function with its arguments arranged according to the specified indexes.
Use Array.reduce() and Array.indexOf() to reorder arguments based on indexes in combination with the spread operator (...) to pass the transformed arguments to fn.
\ No newline at end of file
diff --git a/docs/archive.html b/docs/archive.html
new file mode 100644
index 000000000..e6b71c266
--- /dev/null
+++ b/docs/archive.html
@@ -0,0 +1,242 @@
+Snippets Archive - 30 seconds of code
These snippets, while useful and interesting, didn't quite make it into the repository due to either having very specific use-cases or being outdated. However we felt like they might still be useful to some readers, so here they are.
binarySearch
Use recursion. Similar to Array.indexOf() that finds the index of a value within an array. The difference being this operation only works with sorted arrays which offers a major performance boost due to it's logarithmic nature when compared to a linear search or Array.indexOf().
Search a sorted array by repeatedly dividing the search interval in half. Begin with an interval covering the whole array. If the value of the search is less than the item in the middle of the interval, recurse into the lower half. Otherwise recurse into the upper half. Repeatedly recurse until the value is found which is the mid or you've recursed to a point that is greater than the length which means the value doesn't exist and return -1.
Removes any properties except the ones specified from a JSON object.
Use Object.keys() method to loop over given JSON object and deleting keys that are not included in given array. If you pass a special key,childIndicator, it will search deeply apply the function to inner objects, too.
Returns the array of factors of the given num. If the second argument is set to true returns only the prime factors of num. If num is 1 or 0 returns an empty array. If num is less than 0 returns all the factors of -int together with their additive inverses.
Use Array.from(), Array.map() and Array.filter() to find all the factors of num. If given num is negative, use Array.reduce() to add the additive inverses to the array. Return all results if primes is false, else determine and return only the prime factors using isPrime and Array.filter(). Omit the second argument, primes, to return prime and non-prime factors by default.
Note:- Negative numbers are not considered prime.
constfactors=(num, primes =false)=>{
+ constisPrime= num =>{
+ const boundary = Math.floor(Math.sqrt(num));
+ for(var i =2; i <= boundary; i++)if(num % i ===0)returnfalse;
+ return num >=2;
+ };
+ const isNeg = num <0;
+ num = isNeg ? -num : num;
+ let array = Array.from({ length: num -1})
+ .map((val, i)=>(num %(i +2)===0? i +2:false))
+ .filter(val => val);
+ if(isNeg)
+ array = array.reduce((acc, val)=>{
+ acc.push(val);
+ acc.push(-val);
+ return acc;
+ }, []);
+ return primes ? array.filter(isPrime) : array;
+};
+
Returns the number of fibonnacci numbers up to num(0 and num inclusive).
Use a mathematical formula to calculate the number of fibonacci numbers until num.
constfibonacciCountUntilNum= num =>
+ Math.ceil(Math.log(num * Math.sqrt(5)+1/2)/ Math.log((Math.sqrt(5)+1)/2));
+
fibonacciCountUntilNum(10);// 7
+
fibonacciUntilNum
Generates an array, containing the Fibonacci sequence, up until the nth term.
Create an empty array of the specific length, initializing the first two values (0 and 1). Use Array.reduce() to add values into the array, using the sum of the last two values, except for the first two. Uses a mathematical formula to calculate the length of the array required.
constfibonacciUntilNum= num =>{
+ let n = Math.ceil(Math.log(num * Math.sqrt(5)+1/2)/ Math.log((Math.sqrt(5)+1)/2));
+ return Array.from({ length: n }).reduce(
+ (acc, val, i)=> acc.concat(i >1? acc[i -1]+ acc[i -2] : i),
+ []
+ );
+};
+
Returns the number of times num can be divided by divisor (integer or fractional) without getting a fractional answer. Works for both negative and positive integers.
If divisor is -1 or 1 return Infinity. If divisor is -0 or 0 return 0. Otherwise, keep dividing num with divisor and incrementing i, while the result is an integer. Return the number of times the loop was executed, i.
consthowManyTimes=(num, divisor)=>{
+ if(divisor ===1|| divisor === -1)returnInfinity;
+ if(divisor ===0)return0;
+ let i =0;
+ while(Number.isInteger(num / divisor)) {
+ i++;
+ num = num / divisor;
+ }
+ return i;
+};
+
Use XMLHttpRequest web api to make a delete request to the given url. Handle the onload event, by running the provided callback function. Handle the onerror event, by running the provided err function. Omit the third argument, err to log the request to the console's error stream by default.
httpDelete('https://website.com/users/123', request =>{
+ console.log(request.responseText);
+});// 'Deletes a user from the database'
+
httpPut
Makes a PUT request to the passed URL.
Use XMLHttpRequest web api to make a put request to the given url. Set the value of an HTTP request header with setRequestHeader method. Handle the onload event, by running the provided callback function. Handle the onerror event, by running the provided err function. Omit the last argument, err to log the request to the console's error stream by default.
const password ="fooBaz";
+const data = JSON.stringify(password);
+httpPut('https://website.com/users/123', data, request =>{
+ console.log(request.responseText);
+});// 'Updates a user's password in database'
+
isArmstrongNumber
Checks if the given number is an Armstrong number or not.
Convert the given number into an array of digits. Use the exponent operator (**) to get the appropriate power for each digit and sum them up. If the sum is equal to the number itself, return true otherwise false.
Use String.toLowerCase() to convert both strings to lowercase, then loop through str and determine if it contains all characters of pattern and in the correct order. Adapted from here.
Calculates the number of changes (substitutions, deletions or additions) required to convert string1 to string2. Can also be used to compare two strings as shown in the second example.
Use recursion. Use Array.filter and spread operator (...) to create an array that all elements with values less than the pivot come before the pivot, and all elements with values greater than the pivot come after it. If the parameter desc is truthy, return array sorts in descending order.
constquickSort=([n,...nums], desc)=>
+ isNaN(n)
+ ?[]
+ : [
+ ...quickSort(nums.filter(v =>(desc ? v > n : v <= n)), desc),
+ n,
+ ...quickSort(nums.filter(v =>(!desc ? v > n : v <= n)), desc)
+ ];
+
Solves the given mathematical expression in reverse polish notation. Throws appropriate errors if there are unrecognized symbols or the expression is wrong. The valid operators are :- +,-,*,/,^,** (^&** are the exponential symbols and are same). This snippet does not supports any unary operators.
Use a dictionary, OPERATORS to specify each operator's matching mathematical operation. Use String.replace() with a regular expression to replace ^ with **, String.split() to tokenize the string and Array.filter() to remove empty tokens. Use Array.forEach() to parse each symbol, evaluate it as a numeric value or operator and solve the mathematical expression. Numeric values are converted to floating point numbers and pushed to a stack, while operators are evaluated using the OPERATORS dictionary and pop elements from the stack to apply operations.
constsolveRPN= rpn =>{
+ const OPERATORS ={
+ '*': (a, b)=> a * b,
+ '+': (a, b)=> a + b,
+ '-': (a, b)=> a - b,
+ '/': (a, b)=> a / b,
+ '**': (a, b)=> a ** b
+ };
+ const[stack, solve]=[
+ [],
+ rpn
+ .replace(/\^/g,'**')
+ .split(/\s+/g)
+ .filter(el => !/\s+/.test(el)&& el !=='')
+ ];
+ solve.forEach(symbol =>{
+ if(!isNaN(parseFloat(symbol))&&isFinite(symbol)) {
+ stack.push(symbol);
+ }else if(Object.keys(OPERATORS).includes(symbol)) {
+ const[a, b]=[stack.pop(), stack.pop()];
+ stack.push(OPERATORS[symbol](parseFloat(b),parseFloat(a)));
+ }else{
+ throw`${symbol} is not a recognized symbol`;
+ }
+ });
+ if(stack.length ===1)return stack.pop();
+ else throw`${rpn} is not a proper RPN. Please check it and try again`;
+};
+
Use SpeechSynthesisUtterance.voice and window.speechSynthesis.getVoices() to convert a message to speech. Use window.speechSynthesis.speak() to play the message.
speechSynthesis('Hello, World');// // plays the message
+
\ No newline at end of file
diff --git a/docs/array.html b/docs/array.html
new file mode 100644
index 000000000..97f9ad25d
--- /dev/null
+++ b/docs/array.html
@@ -0,0 +1,521 @@
+Array - 30 seconds of code
Returns true if the provided predicate function returns true for all elements in a collection, false otherwise.
Use Array.every() to test if all elements in the collection return true based on fn. Omit the second argument, fn, to use Boolean as a default.
constall=(arr, fn = Boolean)=> arr.every(fn);
+
all([4,2,3], x => x >1);// true
+all([1,2,3]);// true
+
any
Returns true if the provided predicate function returns true for at least one element in a collection, false otherwise.
Use Array.some() to test if any elements in the collection return true based on fn. Omit the second argument, fn, to use Boolean as a default.
constany=(arr, fn = Boolean)=> arr.some(fn);
+
any([0,1,2,0], x => x >=2);// true
+any([0,0,1,0]);// true
+
bifurcate
Splits values into two groups. If an element in filter is truthy, the corresponding element in the collection belongs to the first group; otherwise, it belongs to the second group.
Use Array.reduce() and Array.push() to add elements to groups, based on filter.
Splits values into two groups according to a predicate function, which specifies which group an element in the input collection belongs to. If the predicate function returns a truthy value, the collection element belongs to the first group; otherwise, it belongs to the second group.
Use Array.reduce() and Array.push() to add elements to groups, based on the value returned by fn for each element.
Chunks an array into smaller arrays of a specified size.
Use Array.from() to create a new array, that fits the number of chunks that will be produced. Use Array.slice() to map each element of the new array to a chunk the length of size. If the original array can't be split evenly, the final chunk will contain the remaining elements.
Groups the elements of an array based on the given function and returns the count of elements in each group.
Use Array.map() to map the values of an array to a function or property name. Use Array.reduce() to create an object, where the keys are produced from the mapped results.
Use Array.reduce() to increment a counter each time you encounter the specific value inside the array.
constcountOccurrences=(arr, val)=> arr.reduce((a, v)=>(v === val ? a +1: a +0),0);
+
countOccurrences([1,1,2,1,2,3],1);// 3
+
deepFlatten
Deep flattens an array.
Use recursion. Use Array.concat() with an empty array ([]) and the spread operator (...) to flatten an array. Recursively flatten each element that is an array.
Returns the difference between two arrays, after applying the provided function to each array element of both.
Create a Set by applying fn to each element in b, then use Array.filter() in combination with fn on a to only keep values not contained in the previously created set.
Removes elements from the end of an array until the passed function returns true. Returns the remaining elements in the array.
Loop through the array, using Array.slice() to drop the last element of the array until the returned value from the function is true. Returns the remaining elements.
Removes elements in an array until the passed function returns true. Returns the remaining elements in the array.
Loop through the array, using Array.slice() to drop the first element of the array until the returned value from the function is true. Returns the remaining elements.
Returns the index of the last element for which the provided function returns a truthy value.
Use Array.map() to map each element to an array with its index and value. Use Array.filter() to remove elements for which fn returns falsey values, Array.slice(-1) to get the last one.
findLastIndex([1,2,3,4], n => n %2===1);// 2 (index of the value 3)
+
flatten
Flattens an array up to the specified depth.
Use recursion, decrementing depth by 1 for each level of depth. Use Array.reduce() and Array.concat() to merge elements or arrays. Base case, for depth equal to 1 stops recursion. Omit the second argument, depth to flatten only to a depth of 1 (single flatten).
forEachRight([1,2,3,4], val => console.log(val));// '4', '3', '2', '1'
+
groupBy
Groups the elements of an array based on the given function.
Use Array.map() to map the values of an array to a function or property name. Use Array.reduce() to create an object, where the keys are produced from the mapped results.
Returns all the elements of an array except the last one.
Use arr.slice(0,-1) to return all but the last element of the array.
constinitial= arr => arr.slice(0,-1);
+
initial([1,2,3]);// [1,2]
+
initialize2DArray
Initializes a 2D array of given width and height and value.
Use Array.map() to generate h rows where each is a new array of size w initialize with value. If the value is not provided, default to null.
constinitialize2DArray=(w, h, val =null)=>
+ Array.from({ length: h }).map(()=> Array.from({ length: w }).fill(val));
+
initialize2DArray(2,2,0);// [[0,0], [0,0]]
+
initializeArrayWithRange
Initializes an array containing the numbers in the specified range where start and end are inclusive with their common difference step.
Use Array.from(Math.ceil((end+1-start)/step)) to create an array of the desired length(the amounts of elements is equal to (end-start)/step or (end+1-start)/step for inclusive end), Array.map() to fill with the desired values in a range. You can omit start to use a default value of 0. You can omit step to use a default value of 1.
Initializes an array containing the numbers in the specified range (in reverse) where start and end are inclusive with their common difference step.
Use Array.from(Math.ceil((end+1-start)/step)) to create an array of the desired length(the amounts of elements is equal to (end-start)/step or (end+1-start)/step for inclusive end), Array.map() to fill with the desired values in a range. You can omit start to use a default value of 0. You can omit step to use a default value of 1.
Returns a list of elements that exist in both arrays, after applying the provided function to each array element of both.
Create a Set by applying fn to all elements in b, then use Array.filter() on a to only keep elements, which produce values contained in b when fn is applied to them.
Returns 1 if the array is sorted in ascending order, -1 if it is sorted in descending order or 0 if it is not sorted.
Calculate the ordering direction for the first two elements. Use Object.entries() to loop over array objects and compare them in pairs. Return 0 if the direction changes or the direction if the last element is reached.
Joins all elements of an array into a string and returns this string. Uses a separator and an end separator.
Use Array.reduce() to combine elements into a string. Omit the second argument, separator, to use a default separator of ','. Omit the third argument, end, to use the same value as separator by default.
const join =(arr, separator =',', end = separator)=>
+ arr.reduce(
+ (acc, val, i)=>
+ i === arr.length -2
+ ? acc + val + end
+ : i === arr.length -1? acc + val : acc + val + separator,
+ ''
+ );
+
Maps the values of an array to an object using a function, where the key-value pairs consist of the original value as the key and the mapped value.
Use an anonymous inner function scope to declare an undefined memory space, using closures to store a return value. Use a new Array to store the array with a map of the function over its data set and a comma operator to return a second step, without needing to move from one context to another (due to closures and order of operations).
constmapObject=(arr, fn)=>
+ (a =>(
+ (a =[arr, arr.map(fn)]), a[0].reduce((acc, val, ind)=>((acc[val]= a[1][ind]), acc), {})
+ ))();
+
constsquareIt= arr =>mapObject(arr, a => a * a);
+squareIt([1,2,3]);// { 1: 1, 2: 4, 3: 9 }
+
maxN
Returns the n maximum elements from the provided array. If n is greater than or equal to the provided array's length, then return the original array(sorted in descending order).
Use Array.sort() combined with the spread operator (...) to create a shallow clone of the array and sort it in descending order. Use Array.slice() to get the specified number of elements. Omit the second argument, n, to get a one-element array.
constmaxN=(arr, n =1)=>[...arr].sort((a, b)=> b - a).slice(0, n);
+
maxN([1,2,3]);// [3]
+maxN([1,2,3],2);// [3,2]
+
minN
Returns the n minimum elements from the provided array. If n is greater than or equal to the provided array's length, then return the original array(sorted in ascending order).
Use Array.sort() combined with the spread operator (...) to create a shallow clone of the array and sort it in ascending order. Use Array.slice() to get the specified number of elements. Omit the second argument, n, to get a one-element array.
constminN=(arr, n =1)=>[...arr].sort((a, b)=> a - b).slice(0, n);
+
minN([1,2,3]);// [1]
+minN([1,2,3],2);// [1,2]
+
none
Returns true if the provided predicate function returns false for all elements in a collection, false otherwise.
Use Array.some() to test if any elements in the collection return true based on fn. Omit the second argument, fn, to use Boolean as a default.
constnone=(arr, fn = Boolean)=> !arr.some(fn);
+
none([0,1,3,0], x => x ==2);// true
+none([0,0,0]);// true
+
nthElement
Returns the nth element of an array.
Use Array.slice() to get an array containing the nth element at the first place. If the index is out of bounds, return []. Omit the second argument, n, to get the first element of the array.
constnthElement=(arr, n =0)=>(n >0? arr.slice(n, n +1) : arr.slice(n))[0];
+
Groups the elements into two arrays, depending on the provided function's truthiness for each element.
Use Array.reduce() to create an array of two arrays. Use Array.push() to add elements for which fn returns true to the first array and elements for which fn returns false to the second one.
⚠️ WARNING: This function's execution time increases exponentially with each array element. Anything more than 8 to 10 entries will cause your browser to hang as it tries to solve all the different combinations.
Generates all permutations of an array's elements (contains duplicates).
Use recursion. For each element in the given array, create all the partial permutations for the rest of its elements. Use Array.map() to combine the element with each partial permutation, then Array.reduce() to combine all permutations in one array. Base cases are for array length equal to 2 or 1.
Mutates the original array to filter out the values specified.
Use Array.filter() and Array.includes() to pull out the values that are not needed. Use Array.length = 0 to mutate the passed in an array by resetting it's length to zero and Array.push() to re-populate it with only the pulled values.
(For a snippet that does not mutate the original array see without)
Mutates the original array to filter out the values at the specified indexes.
Use Array.filter() and Array.includes() to pull out the values that are not needed. Use Array.length = 0 to mutate the passed in an array by resetting it's length to zero and Array.push() to re-populate it with only the pulled values. Use Array.push() to keep track of pulled values
Mutates the original array to filter out the values specified. Returns the removed elements.
Use Array.filter() and Array.includes() to pull out the values that are not needed. Use Array.length = 0 to mutate the passed in an array by resetting it's length to zero and Array.push() to re-populate it with only the pulled values. Use Array.push() to keep track of pulled values
Mutates the original array to filter out the values specified, based on a given iterator function.
Check if the last argument provided in a function. Use Array.map() to apply the iterator function fn to all array elements. Use Array.filter() and Array.includes() to pull out the values that are not needed. Use Array.length = 0 to mutate the passed in an array by resetting it's length to zero and Array.push() to re-populate it with only the pulled values.
Filter an array of objects based on a condition while also filtering out unspecified keys.
Use Array.filter() to filter the array based on the predicate fn so that it returns the objects for which the condition returned a truthy value. On the filtered array, use Array.map() to return the new object using Array.reduce() to filter out the keys which were not supplied as the keys argument.
Returns the minimum/maximum value of an array, after applying the provided function to set comparing rule.
Use Array.reduce() in combination with the comparator function to get the appropriate element in the array. You can omit the second parameter, comparator, to use the default one that returns the minimum element in the array.
const reduceWhich =(arr,comparator=(a, b)=> a - b)=>
+ arr.reduce((a, b)=>(comparator(a, b)>=0? b : a));
+
Removes elements from an array for which the given function returns false.
Use Array.filter() to find array elements that return truthy values and Array.reduce() to remove elements using Array.splice(). The func is invoked with three arguments (value, index, array).
Use Math.random() to generate a random number, multiply it by length and round it of to the nearest whole number using Math.floor(). This method also works with strings.
Gets n random elements at unique keys from array up to the size of array.
Shuffle the array using the Fisher-Yates algorithm. Use Array.slice() to get the first n elements. Omit the second argument, n to get only one element at random from the array.
constsampleSize=([...arr], n =1)=>{
+ let m = arr.length;
+ while(m) {
+ const i = Math.floor(Math.random()* m--);
+ [arr[m], arr[i]]=[arr[i], arr[m]];
+ }
+ return arr.slice(0, n);
+};
+
Returns the lowest index at which value should be inserted into array in order to maintain its sort order, based on a provided iterator function.
Check if the array is sorted in descending order (loosely). Use Array.findIndex() to find the appropriate index where the element should be inserted, based on the iterator function fn.
constsortedIndexBy=(arr, n, fn)=>{
+ const isDescending =fn(arr[0])>fn(arr[arr.length -1]);
+ const val =fn(n);
+ const index = arr.findIndex(el =>(isDescending ? val >=fn(el) : val <=fn(el)));
+ return index === -1? arr.length : index;
+};
+
Returns the highest index at which value should be inserted into array in order to maintain its sort order.
Check if the array is sorted in descending order (loosely). Use Array.reverse() and Array.findIndex() to find the appropriate last index where the element should be inserted.
constsortedLastIndex=(arr, n)=>{
+ const isDescending = arr[0]> arr[arr.length -1];
+ const index = arr.reverse().findIndex(el =>(isDescending ? n <= el : n >= el));
+ return index === -1?0: arr.length - index;
+};
+
sortedLastIndex([10,20,30,30,40],30);// 4
+
sortedLastIndexBy
Returns the highest index at which value should be inserted into array in order to maintain its sort order, based on a provided iterator function.
Check if the array is sorted in descending order (loosely). Use Array.map() to apply the iterator function to all elements of the array. Use Array.reverse() and Array.findIndex() to find the appropriate last index where the element should be inserted, based on the provided iterator function.
constsortedLastIndexBy=(arr, n, fn)=>{
+ const isDescending =fn(arr[0])>fn(arr[arr.length -1]);
+ const val =fn(n);
+ const index = arr
+ .map(fn)
+ .reverse()
+ .findIndex(el =>(isDescending ? val <= el : val >= el));
+ return index === -1?0: arr.length - index;
+};
+
Performs stable sorting of an array, preserving the initial indexes of items when their values are the same. Does not mutate the original array, but returns a new array instead.
Use Array.map() to pair each element of the input array with its corresponding index. Use Array.sort() and a compare function to sort the list, preserving their initial order if the items compared are equal. Use Array.map() to convert back to the initial array items.
Removes elements from the end of an array until the passed function returns true. Returns the removed elements.
Loop through the array, using a for...of loop over Array.keys() until the returned value from the function is true. Return the removed elements, using Array.reverse() and Array.slice().
consttakeRightWhile=(arr, func)=>{
+ for(let i of arr.reverse().keys())
+ if(func(arr[i]))return arr.reverse().slice(arr.length - i, arr.length);
+ return arr;
+};
+
takeRightWhile([1,2,3,4], n => n <3);// [3, 4]
+
takeWhile
Removes elements in an array until the passed function returns true. Returns the removed elements.
Loop through the array, using a for...of loop over Array.keys() until the returned value from the function is true. Return the removed elements, using Array.slice().
consttakeWhile=(arr, func)=>{
+ for(let i of arr.keys())if(func(arr[i]))return arr.slice(0, i);
+ return arr;
+};
+
takeWhile([1,2,3,4], n => n >=3);// [1, 2]
+
union
Returns every element that exists in any of the two arrays once.
Create a Set with all values of a and b and convert to an array.
Returns every element that exists in any of the two arrays once, after applying the provided function to each array element of both.
Create a Set by applying all fn to all values of a. Create a Set from a and all elements in b whose value, after applying fn does not match a value in the previously created set. Return the last set converted to an array.
Use ES6 Set and the ...rest operator to discard all duplicated values.
constuniqueElements= arr =>[...newSet(arr)];
+
uniqueElements([1,2,2,3,4,4,5]);// [1,2,3,4,5]
+
unzip
Creates an array of arrays, ungrouping the elements in an array produced by zip.
Use Math.max.apply() to get the longest subarray in the array, Array.map() to make each element an array. Use Array.reduce() and Array.forEach() to map grouped values to individual arrays.
Creates an array of elements, ungrouping the elements in an array produced by zip and applying the provided function.
Use Math.max.apply() to get the longest subarray in the array, Array.map() to make each element an array. Use Array.reduce() and Array.forEach() to map grouped values to individual arrays. Use Array.map() and the spread operator (...) to apply fn to each individual group of elements.
Creates an array of elements, grouped based on the position in the original arrays.
Use Math.max.apply() to get the longest array in the arguments. Creates an array with that length as return value and use Array.from() with a map-function to create an array of grouped elements. If lengths of the argument-arrays vary, undefined is used where no value could be found.
Given an array of valid property identifiers and an array of values, return an object associating the properties to the values.
Since an object can have undefined values but not undefined property pointers, the array of properties is used to decide the structure of the resulting object using Array.reduce().
Creates an array of elements, grouped based on the position in the original arrays and using function as the last value to specify how grouped values should be combined.
Check if the last argument provided is a function. Use Math.max() to get the longest array in the arguments. Creates an array with that length as return value and use Array.from() with a map-function to create an array of grouped elements. If lengths of the argument-arrays vary, undefined is used where no value could be found. The function is invoked with the elements of each group (...group).
zipWith([1,2], [10,20], [100,200], (a, b, c)=> a + b + c);// [111,222]
+zipWith(
+ [1,2,3],
+ [10,20],
+ [100,200],
+ (a, b, c)=>(a !=null? a :'a')+(b !=null? b :'b')+(c !=null? c :'c')
+);// [111, 222, '3bc']
+
\ No newline at end of file
diff --git a/docs/beginner.html b/docs/beginner.html
new file mode 100644
index 000000000..9c57840f2
--- /dev/null
+++ b/docs/beginner.html
@@ -0,0 +1,138 @@
+Snippets for Beginners - 30 seconds of code
The following section is aimed towards individuals who are at the start of their web developer journey. Each snippet in the next section is simple yet very educational for newcomers. This section is by no means a complete resource for learning modern JavaScript. However, it is enough to grasp some common concepts and use cases. We also strongly recommend checking out MDN web docs as a learning resource.
currentURL
Returns the current URL.
Use window.location.href to get current URL.
constcurrentURL=()=> window.location.href;
+
currentURL();// 'https://google.com'
+
everyNth
Returns every nth element in an array.
Use Array.filter() to create a new array that contains every nth element of a given array.
Use recursion. If n is less than or equal to 1, return 1. Otherwise, return the product of n and the factorial of n - 1. Throws an exception if n is a negative number.
constfactorial= n =>
+ n <0
+ ?(()=>{
+ throw newTypeError('Negative numbers are not allowed!');
+ })()
+ : n <=1?1: n *factorial(n -1);
+
factorial(6);// 720
+
fibonacci
Generates an array, containing the Fibonacci sequence, up until the nth term.
Create an empty array of the specific length, initializing the first two values (0 and 1). Use Array.reduce() to add values into the array, using the sum of the last two values, except for the first two.
Calculates the greatest common divisor between two or more numbers/arrays.
The inner _gcd function uses recursion. Base case is when y equals 0. In this case, return x. Otherwise, return the GCD of y and the remainder of the division x/y.
constgcd=(...arr)=>{
+ const_gcd=(x, y)=>(!y ? x :gcd(y, x % y));
+ return[...arr].reduce((a, b)=>_gcd(a, b));
+};
+
gcd(8,36);// 4
+gcd(...[12,8,32]);// 4
+
getMeridiemSuffixOfInteger
Converts an integer to a suffixed string, adding am or pm based on its value.
Use the modulo operator (%) and conditional checks to transform an integer to a stringified 12-hour format with meridiem suffix.
constgetMeridiemSuffixOfInteger= num =>
+ num ===0|| num ===24
+ ?12+'am'
+ : num ===12?12+'pm': num <12? num %12+'am': num %12+'pm';
+
Returns true if the given number is even, false otherwise.
Checks whether a number is odd or even using the modulo (%) operator. Returns true if the number is even, false if the number is odd.
constisEven= num => num %2===0;
+
isEven(3);// false
+
isPrime
Checks if the provided integer is a prime number.
Check numbers from 2 to the square root of the given number. Return false if any of them divides the given number, else return true, unless the number is less than 2.
constisPrime= num =>{
+ const boundary = Math.floor(Math.sqrt(num));
+ for(var i =2; i <= boundary; i++)if(num % i ===0)returnfalse;
+ return num >=2;
+};
+
isPrime(11);// true
+
last
Returns the last element in an array.
Use arr.length - 1 to compute the index of the last element of the given array and returning it.
constlast= arr => arr[arr.length -1];
+
last([1,2,3]);// 3
+
lcm
Returns the least common multiple of two or more numbers.
Use the greatest common divisor (GCD) formula and the fact that lcm(x,y) = x * y / gcd(x,y) to determine the least common multiple. The GCD formula uses recursion.
constlcm=(...arr)=>{
+ constgcd=(x, y)=>(!y ? x :gcd(y, x % y));
+ const_lcm=(x, y)=> x * y /gcd(x, y);
+ return[...arr].reduce((a, b)=>_lcm(a, b));
+};
+
lcm(12,7);// 84
+lcm(...[1,3,4,5]);// 60
+
maxN
Returns the n maximum elements from the provided array. If n is greater than or equal to the provided array's length, then return the original array(sorted in descending order).
Use Array.sort() combined with the spread operator (...) to create a shallow clone of the array and sort it in descending order. Use Array.slice() to get the specified number of elements. Omit the second argument, n, to get a one-element array.
constmaxN=(arr, n =1)=>[...arr].sort((a, b)=> b - a).slice(0, n);
+
maxN([1,2,3]);// [3]
+maxN([1,2,3],2);// [3,2]
+
minN
Returns the n minimum elements from the provided array. If n is greater than or equal to the provided array's length, then return the original array(sorted in ascending order).
Use Array.sort() combined with the spread operator (...) to create a shallow clone of the array and sort it in ascending order. Use Array.slice() to get the specified number of elements. Omit the second argument, n, to get a one-element array.
constminN=(arr, n =1)=>[...arr].sort((a, b)=> a - b).slice(0, n);
+
minN([1,2,3]);// [1]
+minN([1,2,3],2);// [1,2]
+
nthElement
Returns the nth element of an array.
Use Array.slice() to get an array containing the nth element at the first place. If the index is out of bounds, return []. Omit the second argument, n, to get the first element of the array.
constnthElement=(arr, n =0)=>(n >0? arr.slice(n, n +1) : arr.slice(n))[0];
+
Use Math.random() to generate a random number and map it to the desired range, using Math.floor() to make it an integer.
constrandomIntegerInRange=(min, max)=> Math.floor(Math.random()*(max - min +1))+ min;
+
randomIntegerInRange(0,5);// 2
+
reverseString
Reverses a string.
Use the spread operator (...) and Array.reverse() to reverse the order of the characters in the string. Combine characters to get a string using String.join('').
Use Math.random() to generate a random number, multiply it by length and round it of to the nearest whole number using Math.floor(). This method also works with strings.
Determine if the string's length is greater than num. Return the string truncated to the desired length, with '...' appended to the end or the original string.
consttruncateString=(str, num)=>
+ str.length > num ? str.slice(0, num >3? num -3: num)+'...': str;
+
truncateString('boomerang',7);// 'boom...'
+
\ No newline at end of file
diff --git a/docs/browser.html b/docs/browser.html
new file mode 100644
index 000000000..710bf273d
--- /dev/null
+++ b/docs/browser.html
@@ -0,0 +1,334 @@
+Browser - 30 seconds of code
Copy a string to the clipboard. Only works as a result of user action (i.e. inside a click event listener).
Create a new <textarea> element, fill it with the supplied data and add it to the HTML document. Use Selection.getRangeAt()to store the selected range (if any). Use document.execCommand('copy') to copy to the clipboard. Remove the <textarea> element from the HTML document. Finally, use Selection().addRange() to recover the original selected range (if any).
copyToClipboard('Lorem ipsum');// 'Lorem ipsum' copied to clipboard.
+
createElement
Creates an element from a string (without appending it to the document). If the given string contains multiple elements, only the first one will be returned.
Use document.createElement() to create a new element. Set its innerHTML to the string supplied as the argument. Use ParentNode.firstElementChild to return the element version of the string.
Creates a pub/sub (publish–subscribe) event hub with emit, on, and off methods.
Use Object.create(null) to create an empty hub object that does not inherit properties from Object.prototype. For emit, resolve the array of handlers based on the event argument and then run each one with Array.forEach() by passing in the data as an argument. For on, create an array for the event if it does not yet exist, then use Array.push() to add the handler to the array. For off, use Array.findIndex() to find the index of the handler in the event array and remove it using Array.splice().
consthandler= data => console.log(data);
+const hub =createEventHub();
+let increment =0;
+
+// Subscribe: listen for different types of events
+hub.on('message', handler);
+hub.on('message', ()=> console.log('Message event fired'));
+hub.on('increment', ()=> increment++);
+
+// Publish: emit events to invoke all handlers subscribed to them, passing the data to them as an argument
+hub.emit('message','hello world');// logs 'hello world' and 'Message event fired'
+hub.emit('message', { hello:'world'});// logs the object and 'Message event fired'
+hub.emit('increment');// `increment` variable is now 1
+
+// Unsubscribe: stop a specific handler from listening to the 'message' event
+hub.off('message', handler);
+
currentURL
Returns the current URL.
Use window.location.href to get current URL.
constcurrentURL=()=> window.location.href;
+
currentURL();// 'https://google.com'
+
detectDeviceType
Detects wether the website is being opened in a mobile device or a desktop/laptop.
Use a regular expression to test the navigator.userAgent property to figure out if the device is a mobile device or a desktop/laptop.
Returns true if the element specified is visible in the viewport, false otherwise.
Use Element.getBoundingClientRect() and the window.inner(Width|Height) values to determine if a given element is visible in the viewport. Omit the second argument to determine if the element is entirely visible, or specify true to determine if it is partially visible.
constelementIsVisibleInViewport=(el, partiallyVisible =false)=>{
+ const{ top, left, bottom, right }= el.getBoundingClientRect();
+ const{ innerHeight, innerWidth }= window;
+ return partiallyVisible
+ ?((top >0&& top < innerHeight)||(bottom >0&& bottom < innerHeight))&&
+ ((left >0&& left < innerWidth)||(right >0&& right < innerWidth))
+ : top >=0&& left >=0&& bottom <= innerHeight && right <= innerWidth;
+};
+
// e.g. 100x100 viewport and a 10x10px element at position {top: -1, left: 0, bottom: 9, right: 10}
+elementIsVisibleInViewport(el);// false - (not fully visible)
+elementIsVisibleInViewport(el,true);// true - (partially visible)
+
getScrollPosition
Returns the scroll position of the current page.
Use pageXOffset and pageYOffset if they are defined, otherwise scrollLeft and scrollTop. You can omit el to use a default value of window.
hide(...document.querySelectorAll('img'));// Hides all <img> elements on the page
+
httpsRedirect
Redirects the page to HTTPS if its currently in HTTP. Also, pressing the back button doesn't take it back to the HTTP page as its replaced in the history.
Use location.protocol to get the protocol currently being used. If it's not HTTPS, use location.replace() to replace the existing page with the HTTPS version of the page. Use location.href to get the full address, split it with String.split() and remove the protocol part of the URL.
httpsRedirect();// If you are on http://mydomain.com, you are redirected to https://mydomain.com
+
observeMutationsadvanced
Returns a new MutationObserver and runs the provided callback for each mutation on the specified element.
Use a MutationObserver to observe mutations on the given element. Use Array.forEach() to run the callback for each mutation that is observed. Omit the third argument, options, to use the default options (all true).
const obs =observeMutations(document, console.log);// Logs all mutations that happen on the page
+obs.disconnect();// Disconnects the observer and stops logging mutations on the page
+
off
Removes an event listener from an element.
Use EventTarget.removeEventListener() to remove an event listener from an element. Omit the fourth argument opts to use false or specify it based on the options used when the event listener was added.
constfn=()=> console.log('!');
+document.body.addEventListener('click', fn);
+off(document.body,'click', fn);// no longer logs '!' upon clicking on the page
+
on
Adds an event listener to an element with the ability to use event delegation.
Use EventTarget.addEventListener() to add an event listener to an element. If there is a target property supplied to the options object, ensure the event target matches the target specified and then invoke the callback by supplying the correct this context. Returns a reference to the custom delegator function, in order to be possible to use with off. Omit opts to default to non-delegation behavior and event bubbling.
constfn=()=> console.log('!');
+on(document.body,'click', fn);// logs '!' upon clicking the body
+on(document.body,'click', fn, { target:'p'});// logs '!' upon clicking a `p` element child of the body
+on(document.body,'click', fn, { options:true});// use capturing instead of bubbling
+
onUserInputChangeadvanced
Run the callback whenever the user input type changes (mouse or touch). Useful for enabling/disabling code depending on the input device. This process is dynamic and works with hybrid devices (e.g. touchscreen laptops).
Use two event listeners. Assume mouse input initially and bind a touchstart event listener to the document. On touchstart, add a mousemove event listener to listen for two consecutive mousemove events firing within 20ms, using performance.now(). Run the callback with the input type as an argument in either of these situations.
onUserInputChange(type =>{
+ console.log('The user is now using', type,'as an input method.');
+});
+
prefix
Returns the prefixed version (if necessary) of a CSS property that the browser supports.
Use Array.findIndex() on an array of vendor prefix strings to test if document.body has one of them defined in its CSSStyleDeclaration object, otherwise return null. Use String.charAt() and String.toUpperCase() to capitalize the property, which will be appended to the vendor prefix string.
prefix('appearance');// 'appearance' on a supported browser, otherwise 'webkitAppearance', 'mozAppearance', 'msAppearance' or 'oAppearance'
+
recordAnimationFrames
Invokes the provided callback on each animation frame.
Use recursion. Provided that running is true, continue invoking window.requestAnimationFrame() which invokes the provided callback. Return an object with two methods start and stop to allow manual control of the recording. Omit the second argument, autoStart, to implicitly call start when the function is invoked.
constcb=()=> console.log('Animation frame fired');
+const recorder =recordAnimationFrames(cb);// logs 'Animation frame fired' on each animation frame
+recorder.stop();// stops logging
+recorder.start();// starts again
+const recorder2 =recordAnimationFrames(cb,false);// `start` needs to be explicitly called to begin recording frames
+
redirect
Redirects to a specified URL.
Use window.location.href or window.location.replace() to redirect to url. Pass a second argument to simulate a link click (true - default) or an HTTP redirect (false).
Runs a function in a separate thread by using a Web Worker, allowing long running functions to not block the UI.
Create a new Worker using a Blob object URL, the contents of which should be the stringified version of the supplied function. Immediately post the return value of calling the function back. Return a promise, listening for onmessage and onerror events and resolving the data posted back from the worker, or throwing an error.
constlongRunningFunction=()=>{
+ let result =0;
+ for(let i =0; i <1000; i++) {
+ for(let j =0; j <700; j++) {
+ for(let k =0; k <300; k++) {
+ result = result + i + j + k;
+ }
+ }
+ }
+ return result;
+};
+/*
+ NOTE: Since the function is running in a different context, closures are not supported.
+ The function supplied to `runAsync` gets stringified, so everything becomes literal.
+ All variables and functions must be defined inside.
+*/
+runAsync(longRunningFunction).then(console.log);// 209685000000
+runAsync(()=>10**3).then(console.log);// 1000
+let outsideVariable =50;
+runAsync(()=>typeof outsideVariable).then(console.log);// 'undefined'
+
scrollToTop
Smooth-scrolls to the top of the page.
Get distance from top using document.documentElement.scrollTop or document.body.scrollTop. Scroll by a fraction of the distance from the top. Use window.requestAnimationFrame() to animate the scrolling.
constscrollToTop=()=>{
+ const c = document.documentElement.scrollTop || document.body.scrollTop;
+ if(c >0) {
+ window.requestAnimationFrame(scrollToTop);
+ window.scrollTo(0, c - c /8);
+ }
+};
+
scrollToTop();
+
setStyle
Sets the value of a CSS rule for the specified element.
Use element.style to set the value of the CSS rule for the specified element to val.
show(...document.querySelectorAll('img'));// Shows all <img> elements on the page
+
smoothScroll
Smoothly scrolls the element on which it's called into the visible area of the browser window.
Use .scrollIntoView method to scroll the element. Pass { behavior: 'smooth' } to .scrollIntoView so it scrolls smoothly.
constsmoothScroll= element =>
+ document.querySelector(element).scrollIntoView({
+ behavior:'smooth'
+ });
+
smoothScroll('#fooBar');// scrolls smoothly to the element with the id fooBar
+smoothScroll('.fooBar');// scrolls smoothly to the first element with a class of fooBar
+
toggleClass
Toggle a class for an element.
Use element.classList.toggle() to toggle the specified class for the element.
\ No newline at end of file
diff --git a/docs/date.html b/docs/date.html
new file mode 100644
index 000000000..e435d08d4
--- /dev/null
+++ b/docs/date.html
@@ -0,0 +1,118 @@
+Date - 30 seconds of code
Returns the human readable format of the given number of milliseconds.
Divide ms with the appropriate values to obtain the appropriate values for day, hour, minute, second and millisecond. Use Object.entries() with Array.filter() to keep only non-zero values. Use Array.map() to create the string for each value, pluralizing appropriately. Use String.join(', ') to combine the values into a string.
Results in a string representation of tomorrow's date. Use new Date() to get today's date, adding one day using Date.getDate() and Date.setDate(), and converting the Date object to a string.
consttomorrow=(long =false)=>{
+ let t =newDate();
+ t.setDate(t.getDate()+1);
+ const ret =`${t.getFullYear()}-${String(t.getMonth()+1).padStart(2,'0')}-${String(
+ t.getDate()
+ ).padStart(2,'0')}`;
+ return!long ? ret :`${ret}T00:00:00`;
+};
+
tomorrow();// 2017-12-27 (if current date is 2017-12-26)
+tomorrow(true);// 2017-12-27T00:00:00 (if current date is 2017-12-26)
+
\ No newline at end of file
diff --git a/docs/function.html b/docs/function.html
new file mode 100644
index 000000000..996af8fe8
--- /dev/null
+++ b/docs/function.html
@@ -0,0 +1,272 @@
+Function - 30 seconds of code
Attempts to invoke a function with the provided arguments, returning either the result or the caught error object.
Use a try... catch block to return either the result of the function or an appropriate error.
constattempt=(fn,...args)=>{
+ try{
+ returnfn(...args);
+ }catch(e) {
+ return e instanceofError? e :newError(e);
+ }
+};
+
var elements =attempt(function(selector) {
+ return document.querySelectorAll(selector);
+},'>_>');
+if(elements instanceofError) elements =[];// elements = []
+
bind
Creates a function that invokes fn with a given context, optionally adding any additional supplied parameters to the beginning of the arguments.
Return a function that uses Function.apply() to apply the given context to fn. Use Array.concat() to prepend any additional supplied parameters to the arguments.
Creates a function that invokes the method at a given key of an object, optionally adding any additional supplied parameters to the beginning of the arguments.
Return a function that uses Function.apply() to bind context[fn] to context. Use Array.concat() to prepend any additional supplied parameters to the arguments.
Use Array.reduce() to perform right-to-left function composition. The last (rightmost) function can accept one or more arguments; the remaining functions must be unary.
constadd5= x => x +5;
+constmultiply=(x, y)=> x * y;
+const multiplyAndAdd5 =compose(add5, multiply);
+multiplyAndAdd5(5,2);// 15
+
composeRight
Performs left-to-right function composition.
Use Array.reduce() to perform left-to-right function composition. The first (leftmost) function can accept one or more arguments; the remaining functions must be unary.
constadd=(x, y)=> x + y;
+constsquare= x => x * x;
+const addAndSquare =composeRight(add, square);
+addAndSquare(1,2);// 9
+
converge
Accepts a converging function and a list of branching functions and returns a function that applies each branching function to the arguments and the results of the branching functions are passed as arguments to the converging function.
Use Array.map() and Function.apply() to apply each function to the given arguments. Use the spread operator (...) to call coverger with the results of all other functions.
const average =converge((a, b)=> a / b, [
+ arr => arr.reduce((a, v)=> a + v,0),
+ arr => arr.length
+]);
+average([1,2,3,4,5,6,7]);// 4
+
curry
Curries a function.
Use recursion. If the number of provided arguments (args) is sufficient, call the passed function fn. Otherwise, return a curried function fn that expects the rest of the arguments. If you want to curry a function that accepts a variable number of arguments (a variadic function, e.g. Math.min()), you can optionally pass the number of arguments to the second parameter arity.
Creates a debounced function that delays invoking the provided function until at least ms milliseconds have elapsed since the last time it was invoked.
Each time the debounced function is invoked, clear the current pending timeout with clearTimeout() and use setTimeout() to create a new timeout that delays invoking the function until at least ms milliseconds has elapsed. Use Function.apply() to apply the this context to the function and provide the necessary arguments. Omit the second argument, ms, to set the timeout at a default of 0 ms.
window.addEventListener(
+ 'resize',
+ debounce(()=>{
+ console.log(window.innerWidth);
+ console.log(window.innerHeight);
+ },250)
+);// Will log the window dimensions at most every 250ms
+
defer
Defers invoking a function until the current call stack has cleared.
Use setTimeout() with a timeout of 1ms to add a new event to the browser event queue and allow the rendering engine to complete its work. Use the spread (...) operator to supply the function with an arbitrary number of arguments.
// Example A:
+defer(console.log,'a'), console.log('b');// logs 'b' then 'a'
+
+// Example B:
+document.querySelector('#someElement').innerHTML ='Hello';
+longRunningFunction();//Browser will not update the HTML until this has finished
+defer(longRunningFunction);// Browser will update the HTML then run the function
+
delay
Invokes the provided function after wait milliseconds.
Use setTimeout() to delay execution of fn. Use the spread (...) operator to supply the function with an arbitrary number of arguments.
functionName(Math.max);// max (logged in debug channel of console)
+
memoize
Returns the memoized (cached) function.
Create an empty cache by instantiating a new Map object. Return a function which takes a single argument to be supplied to the memoized function by first checking if the function's output for that specific input value is already cached, or store and return it if not. The function keyword must be used in order to allow the memoized function to have its this context changed if necessary. Allow access to the cache by setting it as a property on the returned function.
// See the `anagrams` snippet.
+const anagramsCached =memoize(anagrams);
+anagramsCached('javascript');// takes a long time
+anagramsCached('javascript');// returns virtually instantly since it's now cached
+console.log(anagramsCached.cache);// The cached anagrams map
+
negate
Negates a predicate function.
Take a predicate function and apply the not operator (!) to it with its arguments.
constnegate= func =>(...args)=> !func(...args);
+
[1,2,3,4,5,6].filter(negate(n => n %2===0));// [ 1, 3, 5 ]
+
once
Ensures a function is called only once.
Utilizing a closure, use a flag, called, and set it to true once the function is called for the first time, preventing it from being called again. In order to allow the function to have its this context changed (such as in an event listener), the function keyword must be used, and the supplied function must have the context applied. Allow the function to be supplied with an arbitrary number of arguments using the rest/spread (...) operator.
constonce= fn =>{
+ let called =false;
+ return function(...args) {
+ if(called)return;
+ called =true;
+ return fn.apply(this, args);
+ };
+};
+
conststartApp=function(event) {
+ console.log(this, event);// document.body, MouseEvent
+};
+document.body.addEventListener('click',once(startApp));// only runs `startApp` once upon click
+
partial
Creates a function that invokes fn with partials prepended to the arguments it receives.
Use the spread operator (...) to prepend partials to the list of arguments of fn.
constdelay= d =>newPromise(r =>setTimeout(r, d));
+runPromisesInSeries([()=>delay(1000), ()=>delay(2000)]);// Executes each promise sequentially, taking a total of 3 seconds to complete
+
sleep
Delays the execution of an asynchronous function.
Delay executing part of an async function, by putting it to sleep, returning a Promise.
constsleep= ms =>newPromise(resolve =>setTimeout(resolve, ms));
+
async functionsleepyWork() {
+ console.log("I'm going to sleep for 1 second.");
+ awaitsleep(1000);
+ console.log('I woke up after 1 second.');
+}
+
throttle
Creates a throttled function that only invokes the provided function at most once per every wait milliseconds
Use setTimeout() and clearTimeout() to throttle the given method, fn. Use Function.apply() to apply the this context to the function and provide the necessary arguments. Use Date.now() to keep track of the last time the throttled function was invoked. Omit the second argument, wait, to set the timeout at a default of 0 ms.
window.addEventListener(
+ 'resize',
+ throttle(function(evt) {
+ console.log(window.innerWidth);
+ console.log(window.innerHeight);
+ },250)
+);// Will log the window dimensions at most every 250ms
+
times
Iterates over a callback n times
Use Function.call() to call fnn times or until it returns false. Omit the last argument, context, to use an undefined object (or the global object in non-strict mode).
consttimes=(n, fn, context = undefined)=>{
+ let i =0;
+ while(fn.call(context, i)!==false&& ++i < n) {}
+};
+
var output ='';
+times(5, i =>(output += i));
+console.log(output);// 01234
+
uncurry
Uncurries a function up to depth n.
Return a variadic function. Use Array.reduce() on the provided arguments to call each subsequent curry level of the function. If the length of the provided arguments is less than n throw an error. Otherwise, call fn with the proper amount of arguments, using Array.slice(0, n). Omit the second argument, n, to uncurry up to depth 1.
constadd= x => y => z => x + y + z;
+const uncurriedAdd =uncurry(add,3);
+uncurriedAdd(1,2,3);// 6
+
unfold
Builds an array, using an iterator function and an initial seed value.
Use a while loop and Array.push() to call the function repeatedly until it returns false. The iterator function accepts one argument (seed) and must always return an array with two elements ([value, nextSeed]) or false to terminate.
constunfold=(fn, seed)=>{
+ let result =[],
+ val =[null, seed];
+ while((val =fn(val[1]))) result.push(val[0]);
+ return result;
+};
+
varf= n =>(n >50?false: [-n, n +10]);
+unfold(f,10);// [-10, -20, -30, -40, -50]
+
\ No newline at end of file
diff --git a/docs/icons/chevron-left.svg b/docs/icons/chevron-left.svg
new file mode 100644
index 000000000..5fa552a07
--- /dev/null
+++ b/docs/icons/chevron-left.svg
@@ -0,0 +1 @@
+
\ No newline at end of file
diff --git a/docs/icons/chevron-right.svg b/docs/icons/chevron-right.svg
new file mode 100644
index 000000000..399d68762
--- /dev/null
+++ b/docs/icons/chevron-right.svg
@@ -0,0 +1 @@
+
\ No newline at end of file
diff --git a/docs/icons/code.svg b/docs/icons/code.svg
new file mode 100644
index 000000000..d66aa59da
--- /dev/null
+++ b/docs/icons/code.svg
@@ -0,0 +1 @@
+
\ No newline at end of file
diff --git a/docs/icons/dashboard.svg b/docs/icons/dashboard.svg
new file mode 100644
index 000000000..8a27ad0ad
--- /dev/null
+++ b/docs/icons/dashboard.svg
@@ -0,0 +1 @@
+
\ No newline at end of file
diff --git a/docs/icons/git-branch.svg b/docs/icons/git-branch.svg
new file mode 100644
index 000000000..279e21c5c
--- /dev/null
+++ b/docs/icons/git-branch.svg
@@ -0,0 +1 @@
+
\ No newline at end of file
diff --git a/docs/icons/law.svg b/docs/icons/law.svg
new file mode 100644
index 000000000..61701b384
--- /dev/null
+++ b/docs/icons/law.svg
@@ -0,0 +1 @@
+
\ No newline at end of file
diff --git a/docs/icons/organization.svg b/docs/icons/organization.svg
new file mode 100644
index 000000000..b968ecfcd
--- /dev/null
+++ b/docs/icons/organization.svg
@@ -0,0 +1 @@
+
\ No newline at end of file
diff --git a/docs/icons/star.svg b/docs/icons/star.svg
new file mode 100644
index 000000000..4a584a3c9
--- /dev/null
+++ b/docs/icons/star.svg
@@ -0,0 +1 @@
+
\ No newline at end of file
diff --git a/docs/index.html b/docs/index.html
index 1078621c4..07fcfad76 100644
--- a/docs/index.html
+++ b/docs/index.html
@@ -1,1678 +1,11 @@
-30 seconds of code
⚠️ WARNING: Snippets are not production ready.
30 seconds of code Curated collection of useful JavaScript snippets that you can understand in 30 seconds or less.
Adapter
ary
Creates a function that accepts up to n arguments, ignoring any additional arguments.
Call the provided function, fn, with up to n arguments, using Array.slice(0,n) and the spread operator (...).
constsquare= n => n * n;
-constdouble= n => n *2;
-const fn =overArgs((x, y)=>[x, y], [square, double]);
-fn(9,3);// [81, 6]
-
pipeAsyncFunctions
Performs left-to-right function composition for asynchronous functions.
Use Array.reduce() with the spread operator (...) to perform left-to-right function composition using Promise.then(). The functions can return a combination of: simple values, Promise's, or they can be defined as async ones returning through await. All functions must be unary.
const sum =pipeAsyncFunctions(
- x => x +1,
- x =>newPromise(resolve =>setTimeout(()=>resolve(x +2),1000)),
- x => x +3,
- async x =>(await x)+4
-);
-(async()=>{
- console.log(awaitsum(5));// 15 (after one second)
-})();
-
pipeFunctions
Performs left-to-right function composition.
Use Array.reduce() with the spread operator (...) to perform left-to-right function composition. The first (leftmost) function can accept one or more arguments; the remaining functions must be unary.
Creates a function that invokes the provided function with its arguments arranged according to the specified indexes.
Use Array.reduce() and Array.indexOf() to reorder arguments based on indexes in combination with the spread operator (...) to pass the transformed arguments to fn.
Returns true if the provided predicate function returns true for all elements in a collection, false otherwise.
Use Array.every() to test if all elements in the collection return true based on fn. Omit the second argument, fn, to use Boolean as a default.
constall=(arr, fn = Boolean)=> arr.every(fn);
-
all([4,2,3], x => x >1);// true
-all([1,2,3]);// true
-
any
Returns true if the provided predicate function returns true for at least one element in a collection, false otherwise.
Use Array.some() to test if any elements in the collection return true based on fn. Omit the second argument, fn, to use Boolean as a default.
constany=(arr, fn = Boolean)=> arr.some(fn);
-
any([0,1,2,0], x => x >=2);// true
-any([0,0,1,0]);// true
-
bifurcate
Splits values into two groups. If an element in filter is truthy, the corresponding element in the collection belongs to the first group; otherwise, it belongs to the second group.
Use Array.reduce() and Array.push() to add elements to groups, based on filter.
Splits values into two groups according to a predicate function, which specifies which group an element in the input collection belongs to. If the predicate function returns a truthy value, the collection element belongs to the first group; otherwise, it belongs to the second group.
Use Array.reduce() and Array.push() to add elements to groups, based on the value returned by fn for each element.
Chunks an array into smaller arrays of a specified size.
Use Array.from() to create a new array, that fits the number of chunks that will be produced. Use Array.slice() to map each element of the new array to a chunk the length of size. If the original array can't be split evenly, the final chunk will contain the remaining elements.
Groups the elements of an array based on the given function and returns the count of elements in each group.
Use Array.map() to map the values of an array to a function or property name. Use Array.reduce() to create an object, where the keys are produced from the mapped results.
Use Array.reduce() to increment a counter each time you encounter the specific value inside the array.
constcountOccurrences=(arr, val)=> arr.reduce((a, v)=>(v === val ? a +1: a +0),0);
-
countOccurrences([1,1,2,1,2,3],1);// 3
-
deepFlatten
Deep flattens an array.
Use recursion. Use Array.concat() with an empty array ([]) and the spread operator (...) to flatten an array. Recursively flatten each element that is an array.
Returns the difference between two arrays, after applying the provided function to each array element of both.
Create a Set by applying fn to each element in b, then use Array.filter() in combination with fn on a to only keep values not contained in the previously created set.
Removes elements from the end of an array until the passed function returns true. Returns the remaining elements in the array.
Loop through the array, using Array.slice() to drop the last element of the array until the returned value from the function is true. Returns the remaining elements.
Removes elements in an array until the passed function returns true. Returns the remaining elements in the array.
Loop through the array, using Array.slice() to drop the first element of the array until the returned value from the function is true. Returns the remaining elements.
Returns the index of the last element for which the provided function returns a truthy value.
Use Array.map() to map each element to an array with its index and value. Use Array.filter() to remove elements for which fn returns falsey values, Array.slice(-1) to get the last one.
findLastIndex([1,2,3,4], n => n %2===1);// 2 (index of the value 3)
-
flatten
Flattens an array up to the specified depth.
Use recursion, decrementing depth by 1 for each level of depth. Use Array.reduce() and Array.concat() to merge elements or arrays. Base case, for depth equal to 1 stops recursion. Omit the second argument, depth to flatten only to a depth of 1 (single flatten).
forEachRight([1,2,3,4], val => console.log(val));// '4', '3', '2', '1'
-
groupBy
Groups the elements of an array based on the given function.
Use Array.map() to map the values of an array to a function or property name. Use Array.reduce() to create an object, where the keys are produced from the mapped results.
Returns all the elements of an array except the last one.
Use arr.slice(0,-1) to return all but the last element of the array.
constinitial= arr => arr.slice(0,-1);
-
initial([1,2,3]);// [1,2]
-
initialize2DArray
Initializes a 2D array of given width and height and value.
Use Array.map() to generate h rows where each is a new array of size w initialize with value. If the value is not provided, default to null.
constinitialize2DArray=(w, h, val =null)=>
- Array.from({ length: h }).map(()=> Array.from({ length: w }).fill(val));
-
initialize2DArray(2,2,0);// [[0,0], [0,0]]
-
initializeArrayWithRange
Initializes an array containing the numbers in the specified range where start and end are inclusive with their common difference step.
Use Array.from(Math.ceil((end+1-start)/step)) to create an array of the desired length(the amounts of elements is equal to (end-start)/step or (end+1-start)/step for inclusive end), Array.map() to fill with the desired values in a range. You can omit start to use a default value of 0. You can omit step to use a default value of 1.
Initializes an array containing the numbers in the specified range (in reverse) where start and end are inclusive with their common difference step.
Use Array.from(Math.ceil((end+1-start)/step)) to create an array of the desired length(the amounts of elements is equal to (end-start)/step or (end+1-start)/step for inclusive end), Array.map() to fill with the desired values in a range. You can omit start to use a default value of 0. You can omit step to use a default value of 1.
Returns a list of elements that exist in both arrays, after applying the provided function to each array element of both.
Create a Set by applying fn to all elements in b, then use Array.filter() on a to only keep elements, which produce values contained in b when fn is applied to them.
Returns 1 if the array is sorted in ascending order, -1 if it is sorted in descending order or 0 if it is not sorted.
Calculate the ordering direction for the first two elements. Use Object.entries() to loop over array objects and compare them in pairs. Return 0 if the direction changes or the direction if the last element is reached.
Joins all elements of an array into a string and returns this string. Uses a separator and an end separator.
Use Array.reduce() to combine elements into a string. Omit the second argument, separator, to use a default separator of ','. Omit the third argument, end, to use the same value as separator by default.
const join =(arr, separator =',', end = separator)=>
- arr.reduce(
- (acc, val, i)=>
- i === arr.length -2
- ? acc + val + end
- : i === arr.length -1? acc + val : acc + val + separator,
- ''
- );
-
Maps the values of an array to an object using a function, where the key-value pairs consist of the original value as the key and the mapped value.
Use an anonymous inner function scope to declare an undefined memory space, using closures to store a return value. Use a new Array to store the array with a map of the function over its data set and a comma operator to return a second step, without needing to move from one context to another (due to closures and order of operations).
constmapObject=(arr, fn)=>
- (a =>(
- (a =[arr, arr.map(fn)]), a[0].reduce((acc, val, ind)=>((acc[val]= a[1][ind]), acc), {})
- ))();
-
constsquareIt= arr =>mapObject(arr, a => a * a);
-squareIt([1,2,3]);// { 1: 1, 2: 4, 3: 9 }
-
maxN
Returns the n maximum elements from the provided array. If n is greater than or equal to the provided array's length, then return the original array(sorted in descending order).
Use Array.sort() combined with the spread operator (...) to create a shallow clone of the array and sort it in descending order. Use Array.slice() to get the specified number of elements. Omit the second argument, n, to get a one-element array.
constmaxN=(arr, n =1)=>[...arr].sort((a, b)=> b - a).slice(0, n);
-
maxN([1,2,3]);// [3]
-maxN([1,2,3],2);// [3,2]
-
minN
Returns the n minimum elements from the provided array. If n is greater than or equal to the provided array's length, then return the original array(sorted in ascending order).
Use Array.sort() combined with the spread operator (...) to create a shallow clone of the array and sort it in ascending order. Use Array.slice() to get the specified number of elements. Omit the second argument, n, to get a one-element array.
constminN=(arr, n =1)=>[...arr].sort((a, b)=> a - b).slice(0, n);
-
minN([1,2,3]);// [1]
-minN([1,2,3],2);// [1,2]
-
none
Returns true if the provided predicate function returns false for all elements in a collection, false otherwise.
Use Array.some() to test if any elements in the collection return true based on fn. Omit the second argument, fn, to use Boolean as a default.
constnone=(arr, fn = Boolean)=> !arr.some(fn);
-
none([0,1,3,0], x => x ==2);// true
-none([0,0,0]);// true
-
nthElement
Returns the nth element of an array.
Use Array.slice() to get an array containing the nth element at the first place. If the index is out of bounds, return []. Omit the second argument, n, to get the first element of the array.
constnthElement=(arr, n =0)=>(n >0? arr.slice(n, n +1) : arr.slice(n))[0];
-
Groups the elements into two arrays, depending on the provided function's truthiness for each element.
Use Array.reduce() to create an array of two arrays. Use Array.push() to add elements for which fn returns true to the first array and elements for which fn returns false to the second one.
⚠️ WARNING: This function's execution time increases exponentially with each array element. Anything more than 8 to 10 entries will cause your browser to hang as it tries to solve all the different combinations.
Generates all permutations of an array's elements (contains duplicates).
Use recursion. For each element in the given array, create all the partial permutations for the rest of its elements. Use Array.map() to combine the element with each partial permutation, then Array.reduce() to combine all permutations in one array. Base cases are for array length equal to 2 or 1.
Mutates the original array to filter out the values specified.
Use Array.filter() and Array.includes() to pull out the values that are not needed. Use Array.length = 0 to mutate the passed in an array by resetting it's length to zero and Array.push() to re-populate it with only the pulled values.
(For a snippet that does not mutate the original array see without)
Mutates the original array to filter out the values at the specified indexes.
Use Array.filter() and Array.includes() to pull out the values that are not needed. Use Array.length = 0 to mutate the passed in an array by resetting it's length to zero and Array.push() to re-populate it with only the pulled values. Use Array.push() to keep track of pulled values
Mutates the original array to filter out the values specified. Returns the removed elements.
Use Array.filter() and Array.includes() to pull out the values that are not needed. Use Array.length = 0 to mutate the passed in an array by resetting it's length to zero and Array.push() to re-populate it with only the pulled values. Use Array.push() to keep track of pulled values
Mutates the original array to filter out the values specified, based on a given iterator function.
Check if the last argument provided in a function. Use Array.map() to apply the iterator function fn to all array elements. Use Array.filter() and Array.includes() to pull out the values that are not needed. Use Array.length = 0 to mutate the passed in an array by resetting it's length to zero and Array.push() to re-populate it with only the pulled values.
Filter an array of objects based on a condition while also filtering out unspecified keys.
Use Array.filter() to filter the array based on the predicate fn so that it returns the objects for which the condition returned a truthy value. On the filtered array, use Array.map() to return the new object using Array.reduce() to filter out the keys which were not supplied as the keys argument.
Returns the minimum/maximum value of an array, after applying the provided function to set comparing rule.
Use Array.reduce() in combination with the comparator function to get the appropriate element in the array. You can omit the second parameter, comparator, to use the default one that returns the minimum element in the array.
const reduceWhich =(arr,comparator=(a, b)=> a - b)=>
- arr.reduce((a, b)=>(comparator(a, b)>=0? b : a));
-
Removes elements from an array for which the given function returns false.
Use Array.filter() to find array elements that return truthy values and Array.reduce() to remove elements using Array.splice(). The func is invoked with three arguments (value, index, array).
Use Math.random() to generate a random number, multiply it by length and round it of to the nearest whole number using Math.floor(). This method also works with strings.
Gets n random elements at unique keys from array up to the size of array.
Shuffle the array using the Fisher-Yates algorithm. Use Array.slice() to get the first n elements. Omit the second argument, n to get only one element at random from the array.
constsampleSize=([...arr], n =1)=>{
- let m = arr.length;
- while(m) {
- const i = Math.floor(Math.random()* m--);
- [arr[m], arr[i]]=[arr[i], arr[m]];
- }
- return arr.slice(0, n);
-};
-
Returns the lowest index at which value should be inserted into array in order to maintain its sort order, based on a provided iterator function.
Check if the array is sorted in descending order (loosely). Use Array.findIndex() to find the appropriate index where the element should be inserted, based on the iterator function fn.
constsortedIndexBy=(arr, n, fn)=>{
- const isDescending =fn(arr[0])>fn(arr[arr.length -1]);
- const val =fn(n);
- const index = arr.findIndex(el =>(isDescending ? val >=fn(el) : val <=fn(el)));
- return index === -1? arr.length : index;
-};
-
Returns the highest index at which value should be inserted into array in order to maintain its sort order.
Check if the array is sorted in descending order (loosely). Use Array.reverse() and Array.findIndex() to find the appropriate last index where the element should be inserted.
constsortedLastIndex=(arr, n)=>{
- const isDescending = arr[0]> arr[arr.length -1];
- const index = arr.reverse().findIndex(el =>(isDescending ? n <= el : n >= el));
- return index === -1?0: arr.length - index;
-};
-
sortedLastIndex([10,20,30,30,40],30);// 4
-
sortedLastIndexBy
Returns the highest index at which value should be inserted into array in order to maintain its sort order, based on a provided iterator function.
Check if the array is sorted in descending order (loosely). Use Array.map() to apply the iterator function to all elements of the array. Use Array.reverse() and Array.findIndex() to find the appropriate last index where the element should be inserted, based on the provided iterator function.
constsortedLastIndexBy=(arr, n, fn)=>{
- const isDescending =fn(arr[0])>fn(arr[arr.length -1]);
- const val =fn(n);
- const index = arr
- .map(fn)
- .reverse()
- .findIndex(el =>(isDescending ? val <= el : val >= el));
- return index === -1?0: arr.length - index;
-};
-
Performs stable sorting of an array, preserving the initial indexes of items when their values are the same. Does not mutate the original array, but returns a new array instead.
Use Array.map() to pair each element of the input array with its corresponding index. Use Array.sort() and a compare function to sort the list, preserving their initial order if the items compared are equal. Use Array.map() to convert back to the initial array items.
Removes elements from the end of an array until the passed function returns true. Returns the removed elements.
Loop through the array, using a for...of loop over Array.keys() until the returned value from the function is true. Return the removed elements, using Array.reverse() and Array.slice().
consttakeRightWhile=(arr, func)=>{
- for(let i of arr.reverse().keys())
- if(func(arr[i]))return arr.reverse().slice(arr.length - i, arr.length);
- return arr;
-};
-
takeRightWhile([1,2,3,4], n => n <3);// [3, 4]
-
takeWhile
Removes elements in an array until the passed function returns true. Returns the removed elements.
Loop through the array, using a for...of loop over Array.keys() until the returned value from the function is true. Return the removed elements, using Array.slice().
consttakeWhile=(arr, func)=>{
- for(let i of arr.keys())if(func(arr[i]))return arr.slice(0, i);
- return arr;
-};
-
takeWhile([1,2,3,4], n => n >=3);// [1, 2]
-
union
Returns every element that exists in any of the two arrays once.
Create a Set with all values of a and b and convert to an array.
Returns every element that exists in any of the two arrays once, after applying the provided function to each array element of both.
Create a Set by applying all fn to all values of a. Create a Set from a and all elements in b whose value, after applying fn does not match a value in the previously created set. Return the last set converted to an array.
Use ES6 Set and the ...rest operator to discard all duplicated values.
constuniqueElements= arr =>[...newSet(arr)];
-
uniqueElements([1,2,2,3,4,4,5]);// [1,2,3,4,5]
-
unzip
Creates an array of arrays, ungrouping the elements in an array produced by zip.
Use Math.max.apply() to get the longest subarray in the array, Array.map() to make each element an array. Use Array.reduce() and Array.forEach() to map grouped values to individual arrays.
Creates an array of elements, ungrouping the elements in an array produced by zip and applying the provided function.
Use Math.max.apply() to get the longest subarray in the array, Array.map() to make each element an array. Use Array.reduce() and Array.forEach() to map grouped values to individual arrays. Use Array.map() and the spread operator (...) to apply fn to each individual group of elements.
Creates an array of elements, grouped based on the position in the original arrays.
Use Math.max.apply() to get the longest array in the arguments. Creates an array with that length as return value and use Array.from() with a map-function to create an array of grouped elements. If lengths of the argument-arrays vary, undefined is used where no value could be found.
Given an array of valid property identifiers and an array of values, return an object associating the properties to the values.
Since an object can have undefined values but not undefined property pointers, the array of properties is used to decide the structure of the resulting object using Array.reduce().
Creates an array of elements, grouped based on the position in the original arrays and using function as the last value to specify how grouped values should be combined.
Check if the last argument provided is a function. Use Math.max() to get the longest array in the arguments. Creates an array with that length as return value and use Array.from() with a map-function to create an array of grouped elements. If lengths of the argument-arrays vary, undefined is used where no value could be found. The function is invoked with the elements of each group (...group).
Copy a string to the clipboard. Only works as a result of user action (i.e. inside a click event listener).
Create a new <textarea> element, fill it with the supplied data and add it to the HTML document. Use Selection.getRangeAt()to store the selected range (if any). Use document.execCommand('copy') to copy to the clipboard. Remove the <textarea> element from the HTML document. Finally, use Selection().addRange() to recover the original selected range (if any).
copyToClipboard('Lorem ipsum');// 'Lorem ipsum' copied to clipboard.
-
createElement
Creates an element from a string (without appending it to the document). If the given string contains multiple elements, only the first one will be returned.
Use document.createElement() to create a new element. Set its innerHTML to the string supplied as the argument. Use ParentNode.firstElementChild to return the element version of the string.
Creates a pub/sub (publish–subscribe) event hub with emit, on, and off methods.
Use Object.create(null) to create an empty hub object that does not inherit properties from Object.prototype. For emit, resolve the array of handlers based on the event argument and then run each one with Array.forEach() by passing in the data as an argument. For on, create an array for the event if it does not yet exist, then use Array.push() to add the handler to the array. For off, use Array.findIndex() to find the index of the handler in the event array and remove it using Array.splice().
consthandler= data => console.log(data);
-const hub =createEventHub();
-let increment =0;
-
-// Subscribe: listen for different types of events
-hub.on('message', handler);
-hub.on('message', ()=> console.log('Message event fired'));
-hub.on('increment', ()=> increment++);
-
-// Publish: emit events to invoke all handlers subscribed to them, passing the data to them as an argument
-hub.emit('message','hello world');// logs 'hello world' and 'Message event fired'
-hub.emit('message', { hello:'world'});// logs the object and 'Message event fired'
-hub.emit('increment');// `increment` variable is now 1
-
-// Unsubscribe: stop a specific handler from listening to the 'message' event
-hub.off('message', handler);
-
currentURL
Returns the current URL.
Use window.location.href to get current URL.
constcurrentURL=()=> window.location.href;
-
currentURL();// 'https://google.com'
-
detectDeviceType
Detects wether the website is being opened in a mobile device or a desktop/laptop.
Use a regular expression to test the navigator.userAgent property to figure out if the device is a mobile device or a desktop/laptop.
Returns true if the element specified is visible in the viewport, false otherwise.
Use Element.getBoundingClientRect() and the window.inner(Width|Height) values to determine if a given element is visible in the viewport. Omit the second argument to determine if the element is entirely visible, or specify true to determine if it is partially visible.
constelementIsVisibleInViewport=(el, partiallyVisible =false)=>{
- const{ top, left, bottom, right }= el.getBoundingClientRect();
- const{ innerHeight, innerWidth }= window;
- return partiallyVisible
- ?((top >0&& top < innerHeight)||(bottom >0&& bottom < innerHeight))&&
- ((left >0&& left < innerWidth)||(right >0&& right < innerWidth))
- : top >=0&& left >=0&& bottom <= innerHeight && right <= innerWidth;
-};
-
// e.g. 100x100 viewport and a 10x10px element at position {top: -1, left: 0, bottom: 9, right: 10}
-elementIsVisibleInViewport(el);// false - (not fully visible)
-elementIsVisibleInViewport(el,true);// true - (partially visible)
-
getScrollPosition
Returns the scroll position of the current page.
Use pageXOffset and pageYOffset if they are defined, otherwise scrollLeft and scrollTop. You can omit el to use a default value of window.
hide(...document.querySelectorAll('img'));// Hides all <img> elements on the page
-
httpsRedirect
Redirects the page to HTTPS if its currently in HTTP. Also, pressing the back button doesn't take it back to the HTTP page as its replaced in the history.
Use location.protocol to get the protocol currently being used. If it's not HTTPS, use location.replace() to replace the existing page with the HTTPS version of the page. Use location.href to get the full address, split it with String.split() and remove the protocol part of the URL.
httpsRedirect();// If you are on http://mydomain.com, you are redirected to https://mydomain.com
-
observeMutationsadvanced
Returns a new MutationObserver and runs the provided callback for each mutation on the specified element.
Use a MutationObserver to observe mutations on the given element. Use Array.forEach() to run the callback for each mutation that is observed. Omit the third argument, options, to use the default options (all true).
const obs =observeMutations(document, console.log);// Logs all mutations that happen on the page
-obs.disconnect();// Disconnects the observer and stops logging mutations on the page
-
off
Removes an event listener from an element.
Use EventTarget.removeEventListener() to remove an event listener from an element. Omit the fourth argument opts to use false or specify it based on the options used when the event listener was added.
constfn=()=> console.log('!');
-document.body.addEventListener('click', fn);
-off(document.body,'click', fn);// no longer logs '!' upon clicking on the page
-
on
Adds an event listener to an element with the ability to use event delegation.
Use EventTarget.addEventListener() to add an event listener to an element. If there is a target property supplied to the options object, ensure the event target matches the target specified and then invoke the callback by supplying the correct this context. Returns a reference to the custom delegator function, in order to be possible to use with off. Omit opts to default to non-delegation behavior and event bubbling.
constfn=()=> console.log('!');
-on(document.body,'click', fn);// logs '!' upon clicking the body
-on(document.body,'click', fn, { target:'p'});// logs '!' upon clicking a `p` element child of the body
-on(document.body,'click', fn, { options:true});// use capturing instead of bubbling
-
onUserInputChangeadvanced
Run the callback whenever the user input type changes (mouse or touch). Useful for enabling/disabling code depending on the input device. This process is dynamic and works with hybrid devices (e.g. touchscreen laptops).
Use two event listeners. Assume mouse input initially and bind a touchstart event listener to the document. On touchstart, add a mousemove event listener to listen for two consecutive mousemove events firing within 20ms, using performance.now(). Run the callback with the input type as an argument in either of these situations.
onUserInputChange(type =>{
- console.log('The user is now using', type,'as an input method.');
-});
-
prefix
Returns the prefixed version (if necessary) of a CSS property that the browser supports.
Use Array.findIndex() on an array of vendor prefix strings to test if document.body has one of them defined in its CSSStyleDeclaration object, otherwise return null. Use String.charAt() and String.toUpperCase() to capitalize the property, which will be appended to the vendor prefix string.
prefix('appearance');// 'appearance' on a supported browser, otherwise 'webkitAppearance', 'mozAppearance', 'msAppearance' or 'oAppearance'
-
recordAnimationFrames
Invokes the provided callback on each animation frame.
Use recursion. Provided that running is true, continue invoking window.requestAnimationFrame() which invokes the provided callback. Return an object with two methods start and stop to allow manual control of the recording. Omit the second argument, autoStart, to implicitly call start when the function is invoked.
constcb=()=> console.log('Animation frame fired');
-const recorder =recordAnimationFrames(cb);// logs 'Animation frame fired' on each animation frame
-recorder.stop();// stops logging
-recorder.start();// starts again
-const recorder2 =recordAnimationFrames(cb,false);// `start` needs to be explicitly called to begin recording frames
-
redirect
Redirects to a specified URL.
Use window.location.href or window.location.replace() to redirect to url. Pass a second argument to simulate a link click (true - default) or an HTTP redirect (false).
Runs a function in a separate thread by using a Web Worker, allowing long running functions to not block the UI.
Create a new Worker using a Blob object URL, the contents of which should be the stringified version of the supplied function. Immediately post the return value of calling the function back. Return a promise, listening for onmessage and onerror events and resolving the data posted back from the worker, or throwing an error.
constlongRunningFunction=()=>{
- let result =0;
- for(let i =0; i <1000; i++) {
- for(let j =0; j <700; j++) {
- for(let k =0; k <300; k++) {
- result = result + i + j + k;
- }
- }
- }
- return result;
-};
-/*
- NOTE: Since the function is running in a different context, closures are not supported.
- The function supplied to `runAsync` gets stringified, so everything becomes literal.
- All variables and functions must be defined inside.
-*/
-runAsync(longRunningFunction).then(console.log);// 209685000000
-runAsync(()=>10**3).then(console.log);// 1000
-let outsideVariable =50;
-runAsync(()=>typeof outsideVariable).then(console.log);// 'undefined'
-
scrollToTop
Smooth-scrolls to the top of the page.
Get distance from top using document.documentElement.scrollTop or document.body.scrollTop. Scroll by a fraction of the distance from the top. Use window.requestAnimationFrame() to animate the scrolling.
constscrollToTop=()=>{
- const c = document.documentElement.scrollTop || document.body.scrollTop;
- if(c >0) {
- window.requestAnimationFrame(scrollToTop);
- window.scrollTo(0, c - c /8);
- }
-};
-
scrollToTop();
-
setStyle
Sets the value of a CSS rule for the specified element.
Use element.style to set the value of the CSS rule for the specified element to val.
show(...document.querySelectorAll('img'));// Shows all <img> elements on the page
-
smoothScroll
Smoothly scrolls the element on which it's called into the visible area of the browser window.
Use .scrollIntoView method to scroll the element. Pass { behavior: 'smooth' } to .scrollIntoView so it scrolls smoothly.
constsmoothScroll= element =>
- document.querySelector(element).scrollIntoView({
- behavior:'smooth'
- });
-
smoothScroll('#fooBar');// scrolls smoothly to the element with the id fooBar
-smoothScroll('.fooBar');// scrolls smoothly to the first element with a class of fooBar
-
toggleClass
Toggle a class for an element.
Use element.classList.toggle() to toggle the specified class for the element.
Returns the human readable format of the given number of milliseconds.
Divide ms with the appropriate values to obtain the appropriate values for day, hour, minute, second and millisecond. Use Object.entries() with Array.filter() to keep only non-zero values. Use Array.map() to create the string for each value, pluralizing appropriately. Use String.join(', ') to combine the values into a string.
Results in a string representation of tomorrow's date. Use new Date() to get today's date, adding one day using Date.getDate() and Date.setDate(), and converting the Date object to a string.
consttomorrow=(long =false)=>{
- let t =newDate();
- t.setDate(t.getDate()+1);
- const ret =`${t.getFullYear()}-${String(t.getMonth()+1).padStart(2,'0')}-${String(
- t.getDate()
- ).padStart(2,'0')}`;
- return!long ? ret :`${ret}T00:00:00`;
-};
-
tomorrow();// 2017-12-27 (if current date is 2017-12-26)
-tomorrow(true);// 2017-12-27T00:00:00 (if current date is 2017-12-26)
-
Function
attempt
Attempts to invoke a function with the provided arguments, returning either the result or the caught error object.
Use a try... catch block to return either the result of the function or an appropriate error.
constattempt=(fn,...args)=>{
- try{
- returnfn(...args);
- }catch(e) {
- return e instanceofError? e :newError(e);
- }
-};
-
var elements =attempt(function(selector) {
- return document.querySelectorAll(selector);
-},'>_>');
-if(elements instanceofError) elements =[];// elements = []
-
bind
Creates a function that invokes fn with a given context, optionally adding any additional supplied parameters to the beginning of the arguments.
Return a function that uses Function.apply() to apply the given context to fn. Use Array.concat() to prepend any additional supplied parameters to the arguments.
Creates a function that invokes the method at a given key of an object, optionally adding any additional supplied parameters to the beginning of the arguments.
Return a function that uses Function.apply() to bind context[fn] to context. Use Array.concat() to prepend any additional supplied parameters to the arguments.
Use Array.reduce() to perform right-to-left function composition. The last (rightmost) function can accept one or more arguments; the remaining functions must be unary.
constcompose=(...fns)=> fns.reduce((f, g)=>(...args)=>f(g(...args)));
+30 seconds of code
30 seconds of code
Curated collection of useful JavaScript snippets that you can understand in 30 seconds or less.
The core goal of 30 seconds of code is to provide a quality resource for beginner and advanced JavaScript developers alike. We want to help improve the JavaScript ecosystem, by lowering the barrier of entry for newcomers and help seasoned veterans pick up new tricks and remember old ones. In order to achieve this, we have collected hundreds of snippets that can be of use in a wide range of situations. We welcome new contributors and we like fresh ideas, as long as the code is short and easy to grasp in about 30 seconds. The only catch, if you may, is that many of our snippets are not perfectly suited for large, enterprise applications and they might not be deemed production-ready.
In order for 30 seconds of code to be as accessible and useful as possible, all of the snippets in the collection are licensed under the CC0-1.0 License, meaning they are absolutely free to use in any project you like. If you like what we do, you can always credit us, but that is not mandatory.
Today's picks
Our sophisticated robot helpers pick new snippets from our collection daily, so that you can discover new snippets to enhance your projects:
compose
Performs right-to-left function composition.
Use Array.reduce() to perform right-to-left function composition. The last (rightmost) function can accept one or more arguments; the remaining functions must be unary.
constadd5= x => x +5;constmultiply=(x, y)=> x * y;const multiplyAndAdd5 =compose(add5, multiply);multiplyAndAdd5(5,2);// 15
-
composeRight
Performs left-to-right function composition.
Use Array.reduce() to perform left-to-right function composition. The first (leftmost) function can accept one or more arguments; the remaining functions must be unary.
constadd=(x, y)=> x + y;
-constsquare= x => x * x;
-const addAndSquare =composeRight(add, square);
-addAndSquare(1,2);// 9
-
converge
Accepts a converging function and a list of branching functions and returns a function that applies each branching function to the arguments and the results of the branching functions are passed as arguments to the converging function.
Use Array.map() and Function.apply() to apply each function to the given arguments. Use the spread operator (...) to call coverger with the results of all other functions.
const average =converge((a, b)=> a / b, [
- arr => arr.reduce((a, v)=> a + v,0),
- arr => arr.length
-]);
-average([1,2,3,4,5,6,7]);// 4
-
curry
Curries a function.
Use recursion. If the number of provided arguments (args) is sufficient, call the passed function fn. Otherwise, return a curried function fn that expects the rest of the arguments. If you want to curry a function that accepts a variable number of arguments (a variadic function, e.g. Math.min()), you can optionally pass the number of arguments to the second parameter arity.
Creates a debounced function that delays invoking the provided function until at least ms milliseconds have elapsed since the last time it was invoked.
Each time the debounced function is invoked, clear the current pending timeout with clearTimeout() and use setTimeout() to create a new timeout that delays invoking the function until at least ms milliseconds has elapsed. Use Function.apply() to apply the this context to the function and provide the necessary arguments. Omit the second argument, ms, to set the timeout at a default of 0 ms.
window.addEventListener(
- 'resize',
- debounce(()=>{
- console.log(window.innerWidth);
- console.log(window.innerHeight);
- },250)
-);// Will log the window dimensions at most every 250ms
-
defer
Defers invoking a function until the current call stack has cleared.
Use setTimeout() with a timeout of 1ms to add a new event to the browser event queue and allow the rendering engine to complete its work. Use the spread (...) operator to supply the function with an arbitrary number of arguments.
// Example A:
-defer(console.log,'a'), console.log('b');// logs 'b' then 'a'
-
-// Example B:
-document.querySelector('#someElement').innerHTML ='Hello';
-longRunningFunction();//Browser will not update the HTML until this has finished
-defer(longRunningFunction);// Browser will update the HTML then run the function
-
delay
Invokes the provided function after wait milliseconds.
Use setTimeout() to delay execution of fn. Use the spread (...) operator to supply the function with an arbitrary number of arguments.
functionName(Math.max);// max (logged in debug channel of console)
-
memoize
Returns the memoized (cached) function.
Create an empty cache by instantiating a new Map object. Return a function which takes a single argument to be supplied to the memoized function by first checking if the function's output for that specific input value is already cached, or store and return it if not. The function keyword must be used in order to allow the memoized function to have its this context changed if necessary. Allow access to the cache by setting it as a property on the returned function.
// See the `anagrams` snippet.
-const anagramsCached =memoize(anagrams);
-anagramsCached('javascript');// takes a long time
-anagramsCached('javascript');// returns virtually instantly since it's now cached
-console.log(anagramsCached.cache);// The cached anagrams map
-
negate
Negates a predicate function.
Take a predicate function and apply the not operator (!) to it with its arguments.
constnegate= func =>(...args)=> !func(...args);
-
[1,2,3,4,5,6].filter(negate(n => n %2===0));// [ 1, 3, 5 ]
-
once
Ensures a function is called only once.
Utilizing a closure, use a flag, called, and set it to true once the function is called for the first time, preventing it from being called again. In order to allow the function to have its this context changed (such as in an event listener), the function keyword must be used, and the supplied function must have the context applied. Allow the function to be supplied with an arbitrary number of arguments using the rest/spread (...) operator.
constonce= fn =>{
- let called =false;
- return function(...args) {
- if(called)return;
- called =true;
- return fn.apply(this, args);
- };
-};
-
conststartApp=function(event) {
- console.log(this, event);// document.body, MouseEvent
-};
-document.body.addEventListener('click',once(startApp));// only runs `startApp` once upon click
-
partial
Creates a function that invokes fn with partials prepended to the arguments it receives.
Use the spread operator (...) to prepend partials to the list of arguments of fn.
constdelay= d =>newPromise(r =>setTimeout(r, d));
-runPromisesInSeries([()=>delay(1000), ()=>delay(2000)]);// Executes each promise sequentially, taking a total of 3 seconds to complete
-
sleep
Delays the execution of an asynchronous function.
Delay executing part of an async function, by putting it to sleep, returning a Promise.
constsleep= ms =>newPromise(resolve =>setTimeout(resolve, ms));
-
async functionsleepyWork() {
- console.log("I'm going to sleep for 1 second.");
- awaitsleep(1000);
- console.log('I woke up after 1 second.');
-}
-
throttle
Creates a throttled function that only invokes the provided function at most once per every wait milliseconds
Use setTimeout() and clearTimeout() to throttle the given method, fn. Use Function.apply() to apply the this context to the function and provide the necessary arguments. Use Date.now() to keep track of the last time the throttled function was invoked. Omit the second argument, wait, to set the timeout at a default of 0 ms.
window.addEventListener(
- 'resize',
- throttle(function(evt) {
- console.log(window.innerWidth);
- console.log(window.innerHeight);
- },250)
-);// Will log the window dimensions at most every 250ms
-
times
Iterates over a callback n times
Use Function.call() to call fnn times or until it returns false. Omit the last argument, context, to use an undefined object (or the global object in non-strict mode).
consttimes=(n, fn, context = undefined)=>{
- let i =0;
- while(fn.call(context, i)!==false&& ++i < n) {}
-};
-
var output ='';
-times(5, i =>(output += i));
-console.log(output);// 01234
-
uncurry
Uncurries a function up to depth n.
Return a variadic function. Use Array.reduce() on the provided arguments to call each subsequent curry level of the function. If the length of the provided arguments is less than n throw an error. Otherwise, call fn with the proper amount of arguments, using Array.slice(0, n). Omit the second argument, n, to uncurry up to depth 1.
constadd= x => y => z => x + y + z;
-const uncurriedAdd =uncurry(add,3);
-uncurriedAdd(1,2,3);// 6
-
unfold
Builds an array, using an iterator function and an initial seed value.
Use a while loop and Array.push() to call the function repeatedly until it returns false. The iterator function accepts one argument (seed) and must always return an array with two elements ([value, nextSeed]) or false to terminate.
constunfold=(fn, seed)=>{
- let result =[],
- val =[null, seed];
- while((val =fn(val[1]))) result.push(val[0]);
- return result;
-};
-
varf= n =>(n >50?false: [-n, n +10]);
-unfold(f,10);// [-10, -20, -30, -40, -50]
-
Math
approximatelyEqual
Checks if two numbers are approximately equal to each other.
Use Math.abs() to compare the absolute difference of the two values to epsilon. Omit the third parameter, epsilon, to use a default value of 0.001.
Returns the average of an array, after mapping each element to a value using the provided function.
Use Array.map() to map each element to the value returned by fn, Array.reduce() to add each value to an accumulator, initialized with a value of 0, divide by the length of the array.
Evaluates the binomial coefficient of two integers n and k.
Use Number.isNaN() to check if any of the two values is NaN. Check if k is less than 0, greater than or equal to n, equal to 1 or n - 1 and return the appropriate result. Check if n - k is less than k and switch their values accordingly. Loop from 2 through k and calculate the binomial coefficient. Use Math.round() to account for rounding errors in the calculation.
constbinomialCoefficient=(n, k)=>{
- if(Number.isNaN(n)|| Number.isNaN(k))returnNaN;
- if(k <0|| k > n)return0;
- if(k ===0|| k === n)return1;
- if(k ===1|| k === n -1)return n;
- if(n - k < k) k = n - k;
- let res = n;
- for(let j =2; j <= k; j++) res *=(n - j +1)/ j;
- return Math.round(res);
-};
-
binomialCoefficient(8,2);// 28
-
clampNumber
Clamps num within the inclusive range specified by the boundary values a and b.
If num falls within the range, return num. Otherwise, return the nearest number in the range.
constclampNumber=(num, a, b)=> Math.max(Math.min(num, Math.max(a, b)), Math.min(a, b));
-
Convert the number to a string, using the spread operator (...) to build an array. Use Array.map() and parseInt() to transform each value to an integer.
constdigitize= n =>[...`${n}`].map(i =>parseInt(i));
-
digitize(123);// [1, 2, 3]
-
distance
Returns the distance between two points.
Use Math.hypot() to calculate the Euclidean distance between two points.
Computes the new ratings between two or more opponents using the Elo rating system. It takes an array of pre-ratings and returns an array containing post-ratings. The array should be ordered from best performer to worst performer (winner -> loser).
Use the exponent ** operator and math operators to compute the expected score (chance of winning). of each opponent and compute the new rating for each. Loop through the ratings, using each permutation to compute the post-Elo rating for each player in a pairwise fashion. Omit the second argument to use the default kFactor of 32.
// Standard 1v1s
-elo([1200,1200]);// [1216, 1184]
-elo([1200,1200],64);// [1232, 1168]
-// 4 player FFA, all same rank
-elo([1200,1200,1200,1200]).map(Math.round);// [1246, 1215, 1185, 1154]
-/*
-For teams, each rating can adjusted based on own team's average rating vs.
-average rating of opposing team, with the score being added to their
-own individual rating by supplying it as the third argument.
-*/
-
factorial
Calculates the factorial of a number.
Use recursion. If n is less than or equal to 1, return 1. Otherwise, return the product of n and the factorial of n - 1. Throws an exception if n is a negative number.
constfactorial= n =>
- n <0
- ?(()=>{
- throw newTypeError('Negative numbers are not allowed!');
- })()
- : n <=1?1: n *factorial(n -1);
-
factorial(6);// 720
-
fibonacci
Generates an array, containing the Fibonacci sequence, up until the nth term.
Create an empty array of the specific length, initializing the first two values (0 and 1). Use Array.reduce() to add values into the array, using the sum of the last two values, except for the first two.
Calculates the greatest common divisor between two or more numbers/arrays.
The inner _gcd function uses recursion. Base case is when y equals 0. In this case, return x. Otherwise, return the GCD of y and the remainder of the division x/y.
constgcd=(...arr)=>{
- const_gcd=(x, y)=>(!y ? x :gcd(y, x % y));
- return[...arr].reduce((a, b)=>_gcd(a, b));
-};
-
gcd(8,36);// 4
-gcd(...[12,8,32]);// 4
-
geometricProgression
Initializes an array containing the numbers in the specified range where start and end are inclusive and the ratio between two terms is step. Returns an error if step equals 1.
Use Array.from(), Math.log() and Math.floor() to create an array of the desired length, Array.map() to fill with the desired values in a range. Omit the second argument, start, to use a default value of 1. Omit the third argument, step, to use a default value of 2.
Calculates the Hamming distance between two values.
Use XOR operator (^) to find the bit difference between the two numbers, convert to a binary string using toString(2). Count and return the number of 1s in the string, using match(/1/g).
Checks if the given number falls within the given range.
Use arithmetic comparison to check if the given number is in the specified range. If the second parameter, end, is not specified, the range is considered to be from 0 to start.
constinRange=(n, start, end =null)=>{
- if(end && start > end) end =[start, (start = end)][0];
- return end ==null? n >=0&& n < start : n >= start && n < end;
-};
-
Returns true if the given number is even, false otherwise.
Checks whether a number is odd or even using the modulo (%) operator. Returns true if the number is even, false if the number is odd.
constisEven= num => num %2===0;
-
isEven(3);// false
-
isPrime
Checks if the provided integer is a prime number.
Check numbers from 2 to the square root of the given number. Return false if any of them divides the given number, else return true, unless the number is less than 2.
constisPrime= num =>{
- const boundary = Math.floor(Math.sqrt(num));
- for(var i =2; i <= boundary; i++)if(num % i ===0)returnfalse;
- return num >=2;
-};
-
isPrime(11);// true
-
lcm
Returns the least common multiple of two or more numbers.
Use the greatest common divisor (GCD) formula and the fact that lcm(x,y) = x * y / gcd(x,y) to determine the least common multiple. The GCD formula uses recursion.
constlcm=(...arr)=>{
- constgcd=(x, y)=>(!y ? x :gcd(y, x % y));
- const_lcm=(x, y)=> x * y /gcd(x, y);
- return[...arr].reduce((a, b)=>_lcm(a, b));
-};
-
lcm(12,7);// 84
-lcm(...[1,3,4,5]);// 60
-
luhnCheck
Implementation of the Luhn Algorithm used to validate a variety of identification numbers, such as credit card numbers, IMEI numbers, National Provider Identifier numbers etc.
Use String.split(''), Array.reverse() and Array.map() in combination with parseInt() to obtain an array of digits. Use Array.splice(0,1) to obtain the last digit. Use Array.reduce() to implement the Luhn Algorithm. Return true if sum is divisible by 10, false otherwise.
constluhnCheck= num =>{
- let arr =(num +'')
- .split('')
- .reverse()
- .map(x =>parseInt(x));
- let lastDigit = arr.splice(0,1)[0];
- let sum = arr.reduce((acc, val, i)=>(i %2!==0? acc + val : acc +(val *2)%9||9),0);
- sum += lastDigit;
- return sum %10===0;
-};
-
Find the middle of the array, use Array.sort() to sort the values. Return the number at the midpoint if length is odd, otherwise the average of the two middle numbers.
Generates primes up to a given number, using the Sieve of Eratosthenes.
Generate an array from 2 to the given number. Use Array.filter() to filter out the values divisible by any number from 2 to the square root of the provided number.
constprimes= num =>{
- let arr = Array.from({ length: num -1}).map((x, i)=> i +2),
- sqroot = Math.floor(Math.sqrt(num)),
- numsTillSqroot = Array.from({ length: sqroot -1}).map((x, i)=> i +2);
- numsTillSqroot.forEach(x =>(arr = arr.filter(y => y % x !==0|| y === x)));
- return arr;
-};
-
primes(10);// [2,3,5,7]
-
radsToDegrees
Converts an angle from radians to degrees.
Use Math.PI and the radian to degree formula to convert the angle from radians to degrees.
constradsToDegrees= rad => rad *180.0/ Math.PI;
-
radsToDegrees(Math.PI /2);// 90
-
randomIntArrayInRange
Returns an array of n random integers in the specified range.
Use Array.from() to create an empty array of the specific length, Math.random() to generate a random number and map it to the desired range, using Math.floor() to make it an integer.
constrandomIntArrayInRange=(min, max, n =1)=>
- Array.from({ length: n }, ()=> Math.floor(Math.random()*(max - min +1))+ min);
-
Use Math.round() and template literals to round the number to the specified number of digits. Omit the second argument, decimals to round to an integer.
Returns the standard deviation of an array of numbers.
Use Array.reduce() to calculate the mean, variance and the sum of the variance of the values, the variance of the values, then determine the standard deviation. You can omit the second argument to get the sample standard deviation or set it to true to get the population standard deviation.
Returns the sum of the powers of all the numbers from start to end (both inclusive).
Use Array.fill() to create an array of all the numbers in the target range, Array.map() and the exponent operator (**) to raise them to power and Array.reduce() to add them together. Omit the second argument, power, to use a default power of 2. Omit the third argument, start, to use a default starting value of 1.
Add special characters to text to print in color in the console (combined with console.log()).
Use template literals and special characters to add the appropriate color code to the string output. For background colors, add a special character that resets the background color at the end of the string.
console.log(colorize('foo').red);// 'foo' (red letters)
-console.log(colorize('foo','bar').bgBlue);// 'foo bar' (blue background)
-console.log(colorize(colorize('foo').yellow,colorize('foo').green).bgWhite);// 'foo bar' (first word in yellow letters, second word in green letters, white background for both)
-
hasFlags
Check if the current process's arguments contain the specified flags.
Use Array.every() and Array.includes() to check if process.argv contains all the specified flags. Use a regular expression to test if the specified flags are prefixed with - or -- and prefix them accordingly.
consthasFlags=(...flags)=>
- flags.every(flag => process.argv.includes(/^-{1,2}/.test(flag)? flag :'--'+ flag));
-
JSONToFile({ test:'is passed'},'testJsonFile');// writes the object to 'testJsonFile.json'
-
readFileLines
Returns an array of lines from the specified file.
Use readFileSync function in fs node package to create a Buffer from a file. convert buffer to string using toString(encoding) function. creating an array from contents of file by spliting file content line by line (each \n).
Use recursion. Use Object.assign() and an empty object ({}) to create a shallow clone of the original. Use Object.keys() and Array.forEach() to determine which key-value pairs need to be deep cloned.
const a ={ foo:'bar', obj: { a:1, b:2} };
-const b =deepClone(a);// a !== b, a.obj !== b.obj
-
defaults
Assigns default values for all properties in an object that are undefined.
Use Object.assign() to create a new empty object and copy the original one to maintain key order, use Array.reverse() and the spread operator ... to combine the default values from left to right, finally use obj again to overwrite properties that originally had a value.
Performs a deep comparison between two values to determine if they are equivalent.
Check if the two values are identical, if they are both Date objects with the same time, using Date.getTime() or if they are both non-object values with an equivalent value (strict comparison). Check if only one value is null or undefined or if their prototypes differ. If none of the above conditions are met, use Object.keys() to check if both values have the same number of keys, then use Array.every() to check if every key in the first value exists in the second one and if they are equivalent by calling this method recursively.
constequals=(a, b)=>{
- if(a === b)returntrue;
- if(a instanceofDate&& b instanceofDate)return a.getTime()=== b.getTime();
- if(!a || !b ||(typeof a !='object'&&typeof b !=='object'))return a === b;
- if(a ===null|| a === undefined || b ===null|| b === undefined)returnfalse;
- if(a.prototype !== b.prototype)returnfalse;
- let keys = Object.keys(a);
- if(keys.length !== Object.keys(b).length)returnfalse;
- return keys.every(k =>equals(a[k], b[k]));
-};
-
Returns the first key that satisfies the provided testing function. Otherwise undefined is returned.
Use Object.keys(obj) to get all the properties of the object, Array.find() to test the provided function for each key-value pair. The callback receives three arguments - the value, the key and the object.
Returns the last key that satisfies the provided testing function. Otherwise undefined is returned.
Use Object.keys(obj) to get all the properties of the object, Array.reverse() to reverse their order and Array.find() to test the provided function for each key-value pair. The callback receives three arguments - the value, the key and the object.
Use recursion. Use Object.keys(obj) combined with Array.reduce() to convert every leaf node to a flattened path node. If the value of a key is an object, the function calls itself with the appropriate prefix to create the path using Object.assign(). Otherwise, it adds the appropriate prefixed key-value pair to the accumulator object. You should always omit the second argument, prefix, unless you want every key to have a prefix.
Iterates over all own properties of an object, running a callback for each one.
Use Object.keys(obj) to get all the properties of the object, Array.forEach() to run the provided function for each key-value pair. The callback receives three arguments - the value, the key and the object.
forOwn({ foo:'bar', a:1}, v => console.log(v));// 'bar', 1
-
forOwnRight
Iterates over all own properties of an object in reverse, running a callback for each one.
Use Object.keys(obj) to get all the properties of the object, Array.reverse() to reverse their order and Array.forEach() to run the provided function for each key-value pair. The callback receives three arguments - the value, the key and the object.
forOwnRight({ foo:'bar', a:1}, v => console.log(v));// 1, 'bar'
-
functions
Returns an array of function property names from own (and optionally inherited) enumerable properties of an object.
Use Object.keys(obj) to iterate over the object's own properties. If inherited is true, use Object.get.PrototypeOf(obj) to also get the object's inherited properties. Use Array.filter() to keep only those properties that are functions. Omit the second argument, inherited, to not include inherited properties by default.
Retrieve a set of properties indicated by the given selectors from an object.
Use Array.map() for each selector, String.replace() to replace square brackets with dots, String.split('.') to split each selector, Array.filter() to remove empty values and Array.reduce() to get the value indicated by it.
const obj ={ selector: { to: { val:'val to select'} }, target: [1,2, { a:'test'}] };
-get(obj,'selector.to.val','target[0]','target[2].a');// ['val to select', 1, 'test']
-
invertKeyValues
Inverts the key-value pairs of an object, without mutating it. The corresponding inverted value of each inverted key is an array of keys responsible for generating the inverted value. If a function is supplied, it is applied to each inverted key.
Use Object.keys() and Array.reduce() to invert the key-value pairs of an object and apply the function provided (if any). Omit the second argument, fn, to get the inverted keys without applying a function to them.
Creates a new object from the specified object, where all the keys are in lowercase.
Use Object.keys() and Array.reduce() to create a new object from the specified object. Convert each key in the original object to lowercase, using String.toLowerCase().
Compares two objects to determine if the first one contains equivalent property values to the second one.
Use Object.keys(source) to get all the keys of the second object, then Array.every(), Object.hasOwnProperty() and strict comparison to determine if all keys exist in the first object and have the same values.
Compares two objects to determine if the first one contains equivalent property values to the second one, based on a provided function.
Use Object.keys(source) to get all the keys of the second object, then Array.every(), Object.hasOwnProperty() and the provided function to determine if all keys exist in the first object and have equivalent values. If no function is provided, the values will be compared using the equality operator.
Creates a new object from the combination of two or more objects.
Use Array.reduce() combined with Object.keys(obj) to iterate over all objects and keys. Use hasOwnProperty() and Array.concat() to append values for keys existing in multiple objects.
Given a flat array of objects linked to one another, it will nest them recursively. Useful for nesting comments, such as the ones on reddit.com.
Use recursion. Use Array.filter() to filter the items where the id matches the link, then Array.map() to map each one to a new object that has a children property which recursively nests the items based on which ones are children of the current item. Omit the second argument, id, to default to null which indicates the object is not linked to another one (i.e. it is a top level object). Omit the third argument, link, to use 'parent_id' as the default property which links the object to another one by its id.
Omits the key-value pairs corresponding to the given keys from an object.
Use Object.keys(obj), Array.filter() and Array.includes() to remove the provided keys. Use Array.reduce() to convert the filtered keys back to an object with the corresponding key-value pairs.
Creates an object composed of the properties the given function returns falsey for. The function is invoked with two arguments: (value, key).
Use Object.keys(obj) and Array.filter()to remove the keys for which fn returns a truthy value. Use Array.reduce() to convert the filtered keys back to an object with the corresponding key-value pairs.
omitBy({ a:1, b:'2', c:3}, x =>typeof x ==='number');// { b: '2' }
-
orderBy
Returns a sorted array of objects ordered by properties and orders.
Uses Array.sort(), Array.reduce() on the props array with a default value of 0, use array destructuring to swap the properties position depending on the order passed. If no orders array is passed it sort by 'asc' by default.
Creates an object composed of the properties the given function returns truthy for. The function is invoked with two arguments: (value, key).
Use Object.keys(obj) and Array.filter()to remove the keys for which fn returns a falsey value. Use Array.reduce() to convert the filtered keys back to an object with the corresponding key-value pairs.
const a ={ x:true, y:1};
-const b =shallowClone(a);// a !== b
-
size
Get size of arrays, objects or strings.
Get type of val (array, object or string). Use length property for arrays. Use length or size value if available or number of keys for objects. Use size of a Blob object created from val for strings.
Split strings into array of characters with split('') and return its length.
constsize= val =>
- Array.isArray(val)
- ? val.length
- : val &&typeof val ==='object'
- ? val.size || val.length || Object.keys(val).length
- :typeof val ==='string'?newBlob([val]).size :0;
-
Use Object.keys(obj) combined with Array.reduce() to convert flattened path node to a leaf node. If the value of a key contains a dot delimiter (.), use Array.split('.'), string transformations and JSON.parse() to create an object, then Object.assign() to create the leaf node. Otherwise, add the appropriate key-value pair to the accumulator object.
Use array destructuring and String.toUpperCase() to capitalize first letter, ...rest to get array of characters after first letter and then Array.join('') to make it a string again. Omit the lowerRest parameter to keep the rest of the string intact, or set it to true to convert to lowercase.
Use array destructuring and String.toLowerCase() to decapitalize first letter, ...rest to get array of characters after first letter and then Array.join('') to make it a string again. Omit the upperRest parameter to keep the rest of the string intact, or set it to true to convert to uppercase.
Use String.replace() with a regexp that matches the characters that need to be escaped, using a callback function to replace each character instance with its associated escaped character using a dictionary (object).
Use String.replace() to remove underscores, hyphens, and spaces and convert words to camelcase. Omit the second argument to use a default separator of _.
Checks if a string is an anagram of another string (case-insensitive, ignores spaces, punctuation and special characters).
Use String.toLowerCase(), String.replace() with an appropriate regular expression to remove unnecessary characters, String.split(''), Array.sort() and Array.join('') on both strings to normalize them, then check if their normalized forms are equal.
Replaces all but the last num of characters with the specified mask character.
Use String.slice() to grab the portion of the characters that need to be masked and use String.replace() with a regexp to replace every character with the mask character. Concatenate the masked characters with the remaining unmasked portion of the string. Omit the second argument, num, to keep a default of 4 characters unmasked. If num is negative, the unmasked characters will be at the start of the string. Omit the third argument, mask, to use a default character of '*' for the mask.
Pads a string on both sides with the specified character, if it's shorter than the specified length.
Use String.padStart() and String.padEnd() to pad both sides of the given string. Omit the third argument, char, to use the whitespace character as the default padding character.
Returns true if the given string is a palindrome, false otherwise.
Convert string String.toLowerCase() and use String.replace() to remove non-alphanumeric characters from it. Then, String.split('') into individual characters, Array.reverse(), String.join('') and compare to the original, unreversed string, after converting it String.tolowerCase().
constpalindrome= str =>{
+
deepFlatten
Deep flattens an array.
Use recursion. Use Array.concat() with an empty array ([]) and the spread operator (...) to flatten an array. Recursively flatten each element that is an array.
Returns true if the given string is a palindrome, false otherwise.
Convert string String.toLowerCase() and use String.replace() to remove non-alphanumeric characters from it. Then, String.split('') into individual characters, Array.reverse(), String.join('') and compare to the original, unreversed string, after converting it String.tolowerCase().
constpalindrome= str =>{const s = str.toLowerCase().replace(/[\W_]/g,'');return(
s ===
@@ -1683,401 +16,79 @@ Foo.prototypeShow examples
palindrome('taco cat');// true
-
pluralize
Returns the singular or plural form of the word based on the input number. If the first argument is an object, it will use a closure by returning a function that can auto-pluralize words that don't simply end in s if the supplied dictionary contains the word.
If num is either -1 or 1, return the singular form of the word. If num is any other number, return the plural form. Omit the third argument to use the default of the singular word + s, or supply a custom pluralized word when necessary. If the first argument is an object, utilize a closure by returning a function which can use the supplied dictionary to resolve the correct plural form of the word.
const pluralize =(val, word, plural = word +'s')=>{
- const _pluralize =(num, word, plural = word +'s')=>
- [1,-1].includes(Number(num))? word : plural;
- if(typeof val ==='object')return(num, word)=>_pluralize(num, word, val[word]);
- return_pluralize(val, word, plural);
-};
-
If you are new to JavaScript, we suggest you start by taking a look at the Beginner's snippets
If you want to level up tour JavaScript skills, check out the full Snippet collection
If you want to see how the project was built and contribute, visit our Github repository
If you want to check out some more complex snippets, you can visit the Archive
Related projects
The idea behind 30 seconds of code has inspired some people to create similar collections in other programming languages and environments. Here are the ones we like the most:
Do you have a cool idea for a new snippet? Maybe some code you use often and is not part of our collection? Contributing to 30 seconds of code is as simple as 1,2,3,4!
Your snippet title must be unique and the same as the name of the implemented function.
Use the snippet description to explain what your snippet does and how it works.
Try to keep the snippet's code short and to the point. Use modern techniques and features.
Remember to provide an example of how your snippet works.
Your snippet should solve a real-world problem, no matter how simple.
Never modify README.md or any of the HTML files.
2
Tag
Run npm run tagger from your terminal, then open the tag_database file and tag your snippet appropriately. Multitagging is also supported, just make sure the first tag you specify is on of the major tags and the one that is most relevant to the implemneted function.
3
Test
You can optionally test your snippet to make our job easier. Simply run npm run tester to generate the test files for your snippet. Find the related folder for you snippet under the test directory and write some tests. Remember to run npm run tester again to make sure your tests are passing.
4
Pull request
If you have done everything mentioned above, you should now have an awesome snippet to add to our collection. Simply start a pull request and follow the guidelines provided. Remember to only submit one snippet per pull request, so that we can quickly evaluate and merge your code into the collection.
If you need additional pointers about writing a snippet, be sure to read the complete contribution guidelines.
\ No newline at end of file
diff --git a/docs/manifest.json b/docs/manifest.json
new file mode 100644
index 000000000..578390978
--- /dev/null
+++ b/docs/manifest.json
@@ -0,0 +1,14 @@
+{
+ "name": "30 seconds of code",
+ "short_name": "30s of code",
+ "start_url": "./index.html",
+ "display": "standalone",
+ "background_color": "#f8f8f8",
+ "theme_color": "#111",
+ "description": "Curated collection of useful JavaScript snippets that you can understand in 30 seconds or less.",
+ "icons": [{
+ "src": "favicon.png",
+ "sizes": "128x128",
+ "type": "image/png"
+ }]
+}
diff --git a/docs/math.html b/docs/math.html
new file mode 100644
index 000000000..f7acff94e
--- /dev/null
+++ b/docs/math.html
@@ -0,0 +1,275 @@
+Math - 30 seconds of code
Returns the average of an array, after mapping each element to a value using the provided function.
Use Array.map() to map each element to the value returned by fn, Array.reduce() to add each value to an accumulator, initialized with a value of 0, divide by the length of the array.
Evaluates the binomial coefficient of two integers n and k.
Use Number.isNaN() to check if any of the two values is NaN. Check if k is less than 0, greater than or equal to n, equal to 1 or n - 1 and return the appropriate result. Check if n - k is less than k and switch their values accordingly. Loop from 2 through k and calculate the binomial coefficient. Use Math.round() to account for rounding errors in the calculation.
constbinomialCoefficient=(n, k)=>{
+ if(Number.isNaN(n)|| Number.isNaN(k))returnNaN;
+ if(k <0|| k > n)return0;
+ if(k ===0|| k === n)return1;
+ if(k ===1|| k === n -1)return n;
+ if(n - k < k) k = n - k;
+ let res = n;
+ for(let j =2; j <= k; j++) res *=(n - j +1)/ j;
+ return Math.round(res);
+};
+
binomialCoefficient(8,2);// 28
+
clampNumber
Clamps num within the inclusive range specified by the boundary values a and b.
If num falls within the range, return num. Otherwise, return the nearest number in the range.
constclampNumber=(num, a, b)=> Math.max(Math.min(num, Math.max(a, b)), Math.min(a, b));
+
Convert the number to a string, using the spread operator (...) to build an array. Use Array.map() and parseInt() to transform each value to an integer.
constdigitize= n =>[...`${n}`].map(i =>parseInt(i));
+
digitize(123);// [1, 2, 3]
+
distance
Returns the distance between two points.
Use Math.hypot() to calculate the Euclidean distance between two points.
Computes the new ratings between two or more opponents using the Elo rating system. It takes an array of pre-ratings and returns an array containing post-ratings. The array should be ordered from best performer to worst performer (winner -> loser).
Use the exponent ** operator and math operators to compute the expected score (chance of winning). of each opponent and compute the new rating for each. Loop through the ratings, using each permutation to compute the post-Elo rating for each player in a pairwise fashion. Omit the second argument to use the default kFactor of 32.
// Standard 1v1s
+elo([1200,1200]);// [1216, 1184]
+elo([1200,1200],64);// [1232, 1168]
+// 4 player FFA, all same rank
+elo([1200,1200,1200,1200]).map(Math.round);// [1246, 1215, 1185, 1154]
+/*
+For teams, each rating can adjusted based on own team's average rating vs.
+average rating of opposing team, with the score being added to their
+own individual rating by supplying it as the third argument.
+*/
+
factorial
Calculates the factorial of a number.
Use recursion. If n is less than or equal to 1, return 1. Otherwise, return the product of n and the factorial of n - 1. Throws an exception if n is a negative number.
constfactorial= n =>
+ n <0
+ ?(()=>{
+ throw newTypeError('Negative numbers are not allowed!');
+ })()
+ : n <=1?1: n *factorial(n -1);
+
factorial(6);// 720
+
fibonacci
Generates an array, containing the Fibonacci sequence, up until the nth term.
Create an empty array of the specific length, initializing the first two values (0 and 1). Use Array.reduce() to add values into the array, using the sum of the last two values, except for the first two.
Calculates the greatest common divisor between two or more numbers/arrays.
The inner _gcd function uses recursion. Base case is when y equals 0. In this case, return x. Otherwise, return the GCD of y and the remainder of the division x/y.
constgcd=(...arr)=>{
+ const_gcd=(x, y)=>(!y ? x :gcd(y, x % y));
+ return[...arr].reduce((a, b)=>_gcd(a, b));
+};
+
gcd(8,36);// 4
+gcd(...[12,8,32]);// 4
+
geometricProgression
Initializes an array containing the numbers in the specified range where start and end are inclusive and the ratio between two terms is step. Returns an error if step equals 1.
Use Array.from(), Math.log() and Math.floor() to create an array of the desired length, Array.map() to fill with the desired values in a range. Omit the second argument, start, to use a default value of 1. Omit the third argument, step, to use a default value of 2.
Calculates the Hamming distance between two values.
Use XOR operator (^) to find the bit difference between the two numbers, convert to a binary string using toString(2). Count and return the number of 1s in the string, using match(/1/g).
Checks if the given number falls within the given range.
Use arithmetic comparison to check if the given number is in the specified range. If the second parameter, end, is not specified, the range is considered to be from 0 to start.
constinRange=(n, start, end =null)=>{
+ if(end && start > end) end =[start, (start = end)][0];
+ return end ==null? n >=0&& n < start : n >= start && n < end;
+};
+
Returns true if the given number is even, false otherwise.
Checks whether a number is odd or even using the modulo (%) operator. Returns true if the number is even, false if the number is odd.
constisEven= num => num %2===0;
+
isEven(3);// false
+
isPrime
Checks if the provided integer is a prime number.
Check numbers from 2 to the square root of the given number. Return false if any of them divides the given number, else return true, unless the number is less than 2.
constisPrime= num =>{
+ const boundary = Math.floor(Math.sqrt(num));
+ for(var i =2; i <= boundary; i++)if(num % i ===0)returnfalse;
+ return num >=2;
+};
+
isPrime(11);// true
+
lcm
Returns the least common multiple of two or more numbers.
Use the greatest common divisor (GCD) formula and the fact that lcm(x,y) = x * y / gcd(x,y) to determine the least common multiple. The GCD formula uses recursion.
constlcm=(...arr)=>{
+ constgcd=(x, y)=>(!y ? x :gcd(y, x % y));
+ const_lcm=(x, y)=> x * y /gcd(x, y);
+ return[...arr].reduce((a, b)=>_lcm(a, b));
+};
+
lcm(12,7);// 84
+lcm(...[1,3,4,5]);// 60
+
luhnCheck
Implementation of the Luhn Algorithm used to validate a variety of identification numbers, such as credit card numbers, IMEI numbers, National Provider Identifier numbers etc.
Use String.split(''), Array.reverse() and Array.map() in combination with parseInt() to obtain an array of digits. Use Array.splice(0,1) to obtain the last digit. Use Array.reduce() to implement the Luhn Algorithm. Return true if sum is divisible by 10, false otherwise.
constluhnCheck= num =>{
+ let arr =(num +'')
+ .split('')
+ .reverse()
+ .map(x =>parseInt(x));
+ let lastDigit = arr.splice(0,1)[0];
+ let sum = arr.reduce((acc, val, i)=>(i %2!==0? acc + val : acc +(val *2)%9||9),0);
+ sum += lastDigit;
+ return sum %10===0;
+};
+
Find the middle of the array, use Array.sort() to sort the values. Return the number at the midpoint if length is odd, otherwise the average of the two middle numbers.
Generates primes up to a given number, using the Sieve of Eratosthenes.
Generate an array from 2 to the given number. Use Array.filter() to filter out the values divisible by any number from 2 to the square root of the provided number.
constprimes= num =>{
+ let arr = Array.from({ length: num -1}).map((x, i)=> i +2),
+ sqroot = Math.floor(Math.sqrt(num)),
+ numsTillSqroot = Array.from({ length: sqroot -1}).map((x, i)=> i +2);
+ numsTillSqroot.forEach(x =>(arr = arr.filter(y => y % x !==0|| y === x)));
+ return arr;
+};
+
primes(10);// [2,3,5,7]
+
radsToDegrees
Converts an angle from radians to degrees.
Use Math.PI and the radian to degree formula to convert the angle from radians to degrees.
constradsToDegrees= rad => rad *180.0/ Math.PI;
+
radsToDegrees(Math.PI /2);// 90
+
randomIntArrayInRange
Returns an array of n random integers in the specified range.
Use Array.from() to create an empty array of the specific length, Math.random() to generate a random number and map it to the desired range, using Math.floor() to make it an integer.
constrandomIntArrayInRange=(min, max, n =1)=>
+ Array.from({ length: n }, ()=> Math.floor(Math.random()*(max - min +1))+ min);
+
Use Math.round() and template literals to round the number to the specified number of digits. Omit the second argument, decimals to round to an integer.
Returns the standard deviation of an array of numbers.
Use Array.reduce() to calculate the mean, variance and the sum of the variance of the values, the variance of the values, then determine the standard deviation. You can omit the second argument to get the sample standard deviation or set it to true to get the population standard deviation.
Returns the sum of the powers of all the numbers from start to end (both inclusive).
Use Array.fill() to create an array of all the numbers in the target range, Array.map() and the exponent operator (**) to raise them to power and Array.reduce() to add them together. Omit the second argument, power, to use a default power of 2. Omit the third argument, start, to use a default starting value of 1.
Add special characters to text to print in color in the console (combined with console.log()).
Use template literals and special characters to add the appropriate color code to the string output. For background colors, add a special character that resets the background color at the end of the string.
console.log(colorize('foo').red);// 'foo' (red letters)
+console.log(colorize('foo','bar').bgBlue);// 'foo bar' (blue background)
+console.log(colorize(colorize('foo').yellow,colorize('foo').green).bgWhite);// 'foo bar' (first word in yellow letters, second word in green letters, white background for both)
+
hasFlags
Check if the current process's arguments contain the specified flags.
Use Array.every() and Array.includes() to check if process.argv contains all the specified flags. Use a regular expression to test if the specified flags are prefixed with - or -- and prefix them accordingly.
consthasFlags=(...flags)=>
+ flags.every(flag => process.argv.includes(/^-{1,2}/.test(flag)? flag :'--'+ flag));
+
JSONToFile({ test:'is passed'},'testJsonFile');// writes the object to 'testJsonFile.json'
+
readFileLines
Returns an array of lines from the specified file.
Use readFileSync function in fs node package to create a Buffer from a file. convert buffer to string using toString(encoding) function. creating an array from contents of file by spliting file content line by line (each \n).
\ No newline at end of file
diff --git a/docs/object.html b/docs/object.html
new file mode 100644
index 000000000..ce9c7460d
--- /dev/null
+++ b/docs/object.html
@@ -0,0 +1,332 @@
+Object - 30 seconds of code
Use recursion. Use Object.assign() and an empty object ({}) to create a shallow clone of the original. Use Object.keys() and Array.forEach() to determine which key-value pairs need to be deep cloned.
const a ={ foo:'bar', obj: { a:1, b:2} };
+const b =deepClone(a);// a !== b, a.obj !== b.obj
+
defaults
Assigns default values for all properties in an object that are undefined.
Use Object.assign() to create a new empty object and copy the original one to maintain key order, use Array.reverse() and the spread operator ... to combine the default values from left to right, finally use obj again to overwrite properties that originally had a value.
Performs a deep comparison between two values to determine if they are equivalent.
Check if the two values are identical, if they are both Date objects with the same time, using Date.getTime() or if they are both non-object values with an equivalent value (strict comparison). Check if only one value is null or undefined or if their prototypes differ. If none of the above conditions are met, use Object.keys() to check if both values have the same number of keys, then use Array.every() to check if every key in the first value exists in the second one and if they are equivalent by calling this method recursively.
constequals=(a, b)=>{
+ if(a === b)returntrue;
+ if(a instanceofDate&& b instanceofDate)return a.getTime()=== b.getTime();
+ if(!a || !b ||(typeof a !='object'&&typeof b !=='object'))return a === b;
+ if(a ===null|| a === undefined || b ===null|| b === undefined)returnfalse;
+ if(a.prototype !== b.prototype)returnfalse;
+ let keys = Object.keys(a);
+ if(keys.length !== Object.keys(b).length)returnfalse;
+ return keys.every(k =>equals(a[k], b[k]));
+};
+
Returns the first key that satisfies the provided testing function. Otherwise undefined is returned.
Use Object.keys(obj) to get all the properties of the object, Array.find() to test the provided function for each key-value pair. The callback receives three arguments - the value, the key and the object.
Returns the last key that satisfies the provided testing function. Otherwise undefined is returned.
Use Object.keys(obj) to get all the properties of the object, Array.reverse() to reverse their order and Array.find() to test the provided function for each key-value pair. The callback receives three arguments - the value, the key and the object.
Use recursion. Use Object.keys(obj) combined with Array.reduce() to convert every leaf node to a flattened path node. If the value of a key is an object, the function calls itself with the appropriate prefix to create the path using Object.assign(). Otherwise, it adds the appropriate prefixed key-value pair to the accumulator object. You should always omit the second argument, prefix, unless you want every key to have a prefix.
Iterates over all own properties of an object, running a callback for each one.
Use Object.keys(obj) to get all the properties of the object, Array.forEach() to run the provided function for each key-value pair. The callback receives three arguments - the value, the key and the object.
forOwn({ foo:'bar', a:1}, v => console.log(v));// 'bar', 1
+
forOwnRight
Iterates over all own properties of an object in reverse, running a callback for each one.
Use Object.keys(obj) to get all the properties of the object, Array.reverse() to reverse their order and Array.forEach() to run the provided function for each key-value pair. The callback receives three arguments - the value, the key and the object.
forOwnRight({ foo:'bar', a:1}, v => console.log(v));// 1, 'bar'
+
functions
Returns an array of function property names from own (and optionally inherited) enumerable properties of an object.
Use Object.keys(obj) to iterate over the object's own properties. If inherited is true, use Object.get.PrototypeOf(obj) to also get the object's inherited properties. Use Array.filter() to keep only those properties that are functions. Omit the second argument, inherited, to not include inherited properties by default.
Retrieve a set of properties indicated by the given selectors from an object.
Use Array.map() for each selector, String.replace() to replace square brackets with dots, String.split('.') to split each selector, Array.filter() to remove empty values and Array.reduce() to get the value indicated by it.
const obj ={ selector: { to: { val:'val to select'} }, target: [1,2, { a:'test'}] };
+get(obj,'selector.to.val','target[0]','target[2].a');// ['val to select', 1, 'test']
+
invertKeyValues
Inverts the key-value pairs of an object, without mutating it. The corresponding inverted value of each inverted key is an array of keys responsible for generating the inverted value. If a function is supplied, it is applied to each inverted key.
Use Object.keys() and Array.reduce() to invert the key-value pairs of an object and apply the function provided (if any). Omit the second argument, fn, to get the inverted keys without applying a function to them.
Creates a new object from the specified object, where all the keys are in lowercase.
Use Object.keys() and Array.reduce() to create a new object from the specified object. Convert each key in the original object to lowercase, using String.toLowerCase().
Compares two objects to determine if the first one contains equivalent property values to the second one.
Use Object.keys(source) to get all the keys of the second object, then Array.every(), Object.hasOwnProperty() and strict comparison to determine if all keys exist in the first object and have the same values.
Compares two objects to determine if the first one contains equivalent property values to the second one, based on a provided function.
Use Object.keys(source) to get all the keys of the second object, then Array.every(), Object.hasOwnProperty() and the provided function to determine if all keys exist in the first object and have equivalent values. If no function is provided, the values will be compared using the equality operator.
Creates a new object from the combination of two or more objects.
Use Array.reduce() combined with Object.keys(obj) to iterate over all objects and keys. Use hasOwnProperty() and Array.concat() to append values for keys existing in multiple objects.
Given a flat array of objects linked to one another, it will nest them recursively. Useful for nesting comments, such as the ones on reddit.com.
Use recursion. Use Array.filter() to filter the items where the id matches the link, then Array.map() to map each one to a new object that has a children property which recursively nests the items based on which ones are children of the current item. Omit the second argument, id, to default to null which indicates the object is not linked to another one (i.e. it is a top level object). Omit the third argument, link, to use 'parent_id' as the default property which links the object to another one by its id.
Omits the key-value pairs corresponding to the given keys from an object.
Use Object.keys(obj), Array.filter() and Array.includes() to remove the provided keys. Use Array.reduce() to convert the filtered keys back to an object with the corresponding key-value pairs.
Creates an object composed of the properties the given function returns falsey for. The function is invoked with two arguments: (value, key).
Use Object.keys(obj) and Array.filter()to remove the keys for which fn returns a truthy value. Use Array.reduce() to convert the filtered keys back to an object with the corresponding key-value pairs.
omitBy({ a:1, b:'2', c:3}, x =>typeof x ==='number');// { b: '2' }
+
orderBy
Returns a sorted array of objects ordered by properties and orders.
Uses Array.sort(), Array.reduce() on the props array with a default value of 0, use array destructuring to swap the properties position depending on the order passed. If no orders array is passed it sort by 'asc' by default.
Creates an object composed of the properties the given function returns truthy for. The function is invoked with two arguments: (value, key).
Use Object.keys(obj) and Array.filter()to remove the keys for which fn returns a falsey value. Use Array.reduce() to convert the filtered keys back to an object with the corresponding key-value pairs.
const a ={ x:true, y:1};
+const b =shallowClone(a);// a !== b
+
size
Get size of arrays, objects or strings.
Get type of val (array, object or string). Use length property for arrays. Use length or size value if available or number of keys for objects. Use size of a Blob object created from val for strings.
Split strings into array of characters with split('') and return its length.
constsize= val =>
+ Array.isArray(val)
+ ? val.length
+ : val &&typeof val ==='object'
+ ? val.size || val.length || Object.keys(val).length
+ :typeof val ==='string'?newBlob([val]).size :0;
+
Use Object.keys(obj) combined with Array.reduce() to convert flattened path node to a leaf node. If the value of a key contains a dot delimiter (.), use Array.split('.'), string transformations and JSON.parse() to create an object, then Object.assign() to create the leaf node. Otherwise, add the appropriate key-value pair to the accumulator object.
\ No newline at end of file
diff --git a/docs/string.html b/docs/string.html
new file mode 100644
index 000000000..1f22cdf4d
--- /dev/null
+++ b/docs/string.html
@@ -0,0 +1,261 @@
+String - 30 seconds of code
Use array destructuring and String.toUpperCase() to capitalize first letter, ...rest to get array of characters after first letter and then Array.join('') to make it a string again. Omit the lowerRest parameter to keep the rest of the string intact, or set it to true to convert to lowercase.
Use array destructuring and String.toLowerCase() to decapitalize first letter, ...rest to get array of characters after first letter and then Array.join('') to make it a string again. Omit the upperRest parameter to keep the rest of the string intact, or set it to true to convert to uppercase.
Use String.replace() with a regexp that matches the characters that need to be escaped, using a callback function to replace each character instance with its associated escaped character using a dictionary (object).
Use String.replace() to remove underscores, hyphens, and spaces and convert words to camelcase. Omit the second argument to use a default separator of _.
Checks if a string is an anagram of another string (case-insensitive, ignores spaces, punctuation and special characters).
Use String.toLowerCase(), String.replace() with an appropriate regular expression to remove unnecessary characters, String.split(''), Array.sort() and Array.join('') on both strings to normalize them, then check if their normalized forms are equal.
Replaces all but the last num of characters with the specified mask character.
Use String.slice() to grab the portion of the characters that need to be masked and use String.replace() with a regexp to replace every character with the mask character. Concatenate the masked characters with the remaining unmasked portion of the string. Omit the second argument, num, to keep a default of 4 characters unmasked. If num is negative, the unmasked characters will be at the start of the string. Omit the third argument, mask, to use a default character of '*' for the mask.
Pads a string on both sides with the specified character, if it's shorter than the specified length.
Use String.padStart() and String.padEnd() to pad both sides of the given string. Omit the third argument, char, to use the whitespace character as the default padding character.
Returns true if the given string is a palindrome, false otherwise.
Convert string String.toLowerCase() and use String.replace() to remove non-alphanumeric characters from it. Then, String.split('') into individual characters, Array.reverse(), String.join('') and compare to the original, unreversed string, after converting it String.tolowerCase().
constpalindrome= str =>{
+ const s = str.toLowerCase().replace(/[\W_]/g,'');
+ return(
+ s ===
+ s
+ .split('')
+ .reverse()
+ .join('')
+ );
+};
+
palindrome('taco cat');// true
+
pluralize
Returns the singular or plural form of the word based on the input number. If the first argument is an object, it will use a closure by returning a function that can auto-pluralize words that don't simply end in s if the supplied dictionary contains the word.
If num is either -1 or 1, return the singular form of the word. If num is any other number, return the plural form. Omit the third argument to use the default of the singular word + s, or supply a custom pluralized word when necessary. If the first argument is an object, utilize a closure by returning a function which can use the supplied dictionary to resolve the correct plural form of the word.
const pluralize =(val, word, plural = word +'s')=>{
+ const _pluralize =(num, word, plural = word +'s')=>
+ [1,-1].includes(Number(num))? word : plural;
+ if(typeof val ==='object')return(num, word)=>_pluralize(num, word, val[word]);
+ return_pluralize(val, word, plural);
+};
+
Use the spread operator (...) and Array.reverse() to reverse the order of the characters in the string. Combine characters to get a string using String.join('').
⚠️ WARNING: This function's execution time increases exponentially with each character. Anything more than 8 to 10 characters will cause your browser to hang as it tries to solve all the different combinations.
Generates all permutations of a string (contains duplicates).
Use recursion. For each letter in the given string, create all the partial permutations for the rest of its letters. Use Array.map() to combine the letter with each partial permutation, then Array.reduce() to combine all permutations in one array. Base cases are for string length equal to 2 or 1.
toCamelCase('some_database_field_name');// 'someDatabaseFieldName'
+toCamelCase('Some label that needs to be camelized');// 'someLabelThatNeedsToBeCamelized'
+toCamelCase('some-javascript-property');// 'someJavascriptProperty'
+toCamelCase('some-mixed_string with spaces_underscores-and-hyphens');// 'someMixedStringWithSpacesUnderscoresAndHyphens'
+
toKebabCase
Converts a string to kebab case.
Break the string into words and combine them adding - as a separator, using a regexp.
Determine if the string's length is greater than num. Return the string truncated to the desired length, with '...' appended to the end or the original string.
consttruncateString=(str, num)=>
+ str.length > num ? str.slice(0, num >3? num -3: num)+'...': str;
+
truncateString('boomerang',7);// 'boom...'
+
unescapeHTML
Unescapes escaped HTML characters.
Use String.replace() with a regex that matches the characters that need to be unescaped, using a callback function to replace each escaped character instance with its associated unescaped character using a dictionary (object).
unescapeHTML('<a href="#">Me & you</a>');// '<a href="#">Me & you</a>'
+
URLJoin
Joins all given URL segments together, then normalizes the resulting URL.
Use String.join('/') to combine URL segments, then a series of String.replace() calls with various regexps to normalize the resulting URL (remove double slashes, add proper slashes for protocol, remove slashes before parameters, combine parameters with '&' and normalize first parameter delimiter).
Use String.split() with a supplied pattern (defaults to non-alpha as a regexp) to convert to an array of strings. Use Array.filter() to remove any empty strings. Omit the second argument to use the default regexp.
const words =(str, pattern =/[^a-zA-Z-]+/)=> str.split(pattern).filter(Boolean);
+
\ No newline at end of file
diff --git a/docs/type.html b/docs/type.html
new file mode 100644
index 000000000..d79b0c8c7
--- /dev/null
+++ b/docs/type.html
@@ -0,0 +1,181 @@
+Type - 30 seconds of code
Checks if the provided argument is array-like (i.e. is iterable).
Use the spread operator (...) to check if the provided argument is iterable inside a try... catch block and the comma operator (,) to return the appropriate value.
Returns true if the a value is an empty object, collection, map or set, has no enumerable properties or is any type that is not considered a collection.
Check if the provided value is null or if its length is equal to 0.
constisEmpty= val => val ==null|| !(Object.keys(val)|| val).length;
+
isEmpty(newMap());// true
+isEmpty(newSet());// true
+isEmpty([]);// true
+isEmpty({});// true
+isEmpty('');// true
+isEmpty([1,2]);// false
+isEmpty({ a:1, b:2});// false
+isEmpty('text');// false
+isEmpty(123);// true - type is not considered a collection
+isEmpty(true);// true - type is not considered a collection
+
isFunction
Checks if the given argument is a function.
Use typeof to check if a value is classified as a function primitive.
constisFunction= val =>typeof val ==='function';
+
Returns true if the specified value is null or undefined, false otherwise.
Use the strict equality operator to check if the value and of val are equal to null or undefined.
constisNil= val => val === undefined || val ===null;
+
isNil(null);// true
+isNil(undefined);// true
+
isNull
Returns true if the specified value is null, false otherwise.
Use the strict equality operator to check if the value and of val are equal to null.
constisNull= val => val ===null;
+
isNull(null);// true
+
isNumber
Checks if the given argument is a number.
Use typeof to check if a value is classified as a number primitive.
constisNumber= val =>typeof val ==='number';
+
isNumber('1');// false
+isNumber(1);// true
+
isObject
Returns a boolean determining if the passed value is an object or not.
Uses the Object constructor to create an object wrapper for the given value. If the value is null or undefined, create and return an empty object. Οtherwise, return an object of a type that corresponds to the given value.
Returns a boolean determining if the passed value is primitive or not.
Use Array.includes() on an array of type strings which are not primitive, supplying the type using typeof. Since typeof null evaluates to 'object', it needs to be directly compared.
constisPrimitive= val => !['object','function'].includes(typeof val)|| val ===null;
+
\ No newline at end of file
diff --git a/docs/utility.html b/docs/utility.html
new file mode 100644
index 000000000..fc656d644
--- /dev/null
+++ b/docs/utility.html
@@ -0,0 +1,272 @@
+Utility - 30 seconds of code
Extends a 3-digit color code to a 6-digit color code.
Use Array.map(), String.split() and Array.join() to join the mapped array for converting a 3-digit RGB notated hexadecimal color-code to the 6-digit form. Array.slice() is used to remove # from string start since it's added once.
Returns an object containing the parameters of the current URL.
Use String.match() with an appropriate regular expression to get all key-value pairs, Array.reduce() to map and combine them into a single object. Pass location.search as the argument to apply to the current url.
Converts a color code to a rgb() or rgba() string if alpha value is provided.
Use bitwise right-shift operator and mask bits with & (and) operator to convert a hexadecimal color code (with or without prefixed with #) to a string with the RGB values. If it's 3-digit color code, first convert to 6-digit version. If an alpha value is provided alongside 6-digit hex, give rgba() string in return.
Use XMLHttpRequest web api to make a get request to the given url. Handle the onload event, by calling the given callback the responseText. Handle the onerror event, by running the provided err function. Omit the third argument, err, to log errors to the console's error stream by default.
httpGet(
+ 'https://jsonplaceholder.typicode.com/posts/1',
+ console.log
+);/*
+Logs: {
+ "userId": 1,
+ "id": 1,
+ "title": "sunt aut facere repellat provident occaecati excepturi optio reprehenderit",
+ "body": "quia et suscipit\nsuscipit recusandae consequuntur expedita et cum\nreprehenderit molestiae ut ut quas totam\nnostrum rerum est autem sunt rem eveniet architecto"
+}
+*/
+
httpPost
Makes a POST request to the passed URL.
Use XMLHttpRequest web api to make a post request to the given url. Set the value of an HTTP request header with setRequestHeader method. Handle the onload event, by calling the given callback the responseText. Handle the onerror event, by running the provided err function. Omit the third argument, data, to send no data to the provided url. Omit the fourth argument, err, to log errors to the console's error stream by default.
Determines if the current runtime environment is a browser so that front-end modules can run on the server (Node) without throwing errors.
Use Array.includes() on the typeof values of both window and document (globals usually only available in a browser environment unless they were explicitly defined), which will return true if one of them is undefined. typeof allows globals to be checked for existence without throwing a ReferenceError. If both of them are not undefined, then the current environment is assumed to be a browser.
Returns the index of the function in an array of functions which executed the fastest.
Use Array.map() to generate an array where each value is the total time taken to execute the function after iterations times. Use the difference in performance.now() values before and after to get the total time in milliseconds to a high degree of accuracy. Use Math.min() to find the minimum execution time, and return the index of that shortest time which corresponds to the index of the most performant function. Omit the second argument, iterations, to use a default of 10,000 iterations. The more iterations, the more reliable the result but the longer it will take.
constmostPerformant=(fns, iterations =10000)=>{
+ const times = fns.map(fn =>{
+ const before = performance.now();
+ for(let i =0; i < iterations; i++)fn();
+ return performance.now()- before;
+ });
+ return times.indexOf(Math.min(...times));
+};
+
mostPerformant([
+ ()=>{
+ // Loops through the entire array before returning `false`
+ [1,2,3,4,5,6,7,8,9,'10'].every(el =>typeof el ==='number');
+ },
+ ()=>{
+ // Only needs to reach index `1` before returning false
+ [1,'2',3,4,5,6,7,8,9,10].every(el =>typeof el ==='number');
+ }
+]);// 1
+
nthArg
Creates a function that gets the argument at index n. If n is negative, the nth argument from the end is returned.
Use Array.slice() to get the desired argument at index n.
constnthArg= n =>(...args)=> args.slice(n)[0];
+
const third =nthArg(2);
+third(1,2,3);// 3
+third(1,2);// undefined
+const last =nthArg(-1);
+last(1,2,3,4,5);// 5
+
parseCookie
Parse an HTTP Cookie header string and return an object of all cookie name-value pairs.
Use String.split(';') to separate key-value pairs from each other. Use Array.map() and String.split('=') to separate keys from values in each pair. Use Array.reduce() and decodeURIComponent() to create an object with all key-value pairs.
Converts a number in bytes to a human-readable string.
Use an array dictionary of units to be accessed based on the exponent. Use Number.toPrecision() to truncate the number to a certain number of digits. Return the prettified string by building it up, taking into account the supplied options and whether it is negative or not. Omit the second argument, precision, to use a default precision of 3 digits. Omit the third argument, addSpace, to add space between the number and unit by default.
Use Math.random to generate a random 24-bit(6x4bits) hexadecimal number. Use bit shifting and then convert it to an hexadecimal String using toString(16).
constrandomHexColorCode=()=>{
+ let n =(Math.random()*0xfffff*1000000).toString(16);
+ return'#'+ n.slice(0,6);
+};
+
randomHexColorCode();// "#e34155"
+
RGBToHex
Converts the values of RGB components to a color code.
Convert given RGB parameters to hexadecimal string using bitwise left-shift operator (<<) and toString(16), then String.padStart(6,'0') to get a 6-digit hexadecimal value.
toCurrency(123456.789,'EUR');// €123,456.79 | currency: Euro | currencyLangFormat: Local
+toCurrency(123456.789,'USD','en-us');// $123,456.79 | currency: US Dollar | currencyLangFormat: English (United States)
+toCurrency(123456.789,'USD','fa');// ۱۲۳٬۴۵۶٫۷۹ $ | currency: US Dollar | currencyLangFormat: Farsi
+toCurrency(322342436423.2435,'JPY');// ¥322,342,436,423 | currency: Japanese Yen | currencyLangFormat: Local
+toCurrency(322342436423.2435,'JPY','fi');// 322 342 436 423 ¥ | currency: Japanese Yen | currencyLangFormat: Finnish
+
toDecimalMark
Use toLocaleString() to convert a float-point arithmetic to the Decimal mark form. It makes a comma separated string from a number.
consttoDecimalMark= num => num.toLocaleString('en-US');
+
Use the modulo operator (%) to find values of single and tens digits. Find which ordinal pattern digits match. If digit is found in teens pattern, use teens ordinal.
consttoOrdinalSuffix= num =>{
+ const int =parseInt(num),
+ digits =[int %10, int %100],
+ ordinals =['st','nd','rd','th'],
+ oPattern =[1,2,3,4],
+ tPattern =[11,12,13,14,15,16,17,18,19];
+ return oPattern.includes(digits[0])&& !tPattern.includes(digits[1])
+ ? int + ordinals[digits[0]-1]
+ : int + ordinals[3];
+};
+
toOrdinalSuffix('123');// "123rd"
+
validateNumber
Returns true if the given value is a number, false otherwise.
Use !isNaN() in combination with parseFloat() to check if the argument is a number. Use isFinite() to check if the number is finite. Use Number() to check if the coercion holds.
constvalidateNumber= n => !isNaN(parseFloat(n))&&isFinite(n)&&Number(n)== n;
+
validateNumber('10');// true
+
yesNo
Returns true if the string is y/yes or false if the string is n/no.
Use RegExp.test() to check if the string evaluates to y/yes or n/no. Omit the second argument, def to set the default answer as no.
These snippets, while useful and interesting, didn't quite make it into the repository due to either having very specific use-cases or being outdated. However we felt like they might still be useful to some readers, so here they are.
+
+
diff --git a/static-parts/beginner-page-end.html b/static-parts/beginner-page-end.html
new file mode 100644
index 000000000..0b7d71155
--- /dev/null
+++ b/static-parts/beginner-page-end.html
@@ -0,0 +1,7 @@
+
The following section is aimed towards individuals who are at the start of their web developer journey. Each snippet in the next section is simple yet very educational for newcomers. This section is by no means a complete resource for learning modern JavaScript. However, it is enough to grasp some common concepts and use cases. We also strongly recommend checking out MDN web docs as a learning resource.
The core goal of 30 seconds of code is to provide a quality resource for beginner and advanced JavaScript developers alike. We want to help improve the JavaScript ecosystem, by lowering the barrier of entry for newcomers and help seasoned veterans pick up new tricks and remember old ones. In order to achieve this, we have collected hundreds of snippets that can be of use in a wide range of situations. We welcome new contributors and we like fresh ideas, as long as the code is short and easy to grasp in about 30 seconds. The only catch, if you may, is that many of our snippets are not perfectly suited for large, enterprise applications and they might not be deemed production-ready.
+
+
+
+
+
+
+
+
+
In order for 30 seconds of code to be as accessible and useful as possible, all of the snippets in the collection are licensed under the CC0-1.0 License, meaning they are absolutely free to use in any project you like. If you like what we do, you can always credit us, but that is not mandatory.
+
+
+
+
+
+
+
Today's picks
+
Our sophisticated robot helpers pick new snippets from our collection daily, so that you can discover new snippets to enhance your projects:
+
+
+
+ $daily-picks
+
+
+
+
+
+
+
+
+
Getting started
+
+
If you are new to JavaScript, we suggest you start by taking a look at the Beginner's snippets
+
If you want to level up tour JavaScript skills, check out the full Snippet collection
+
If you want to see how the project was built and contribute, visit our Github repository
+
If you want to check out some more complex snippets, you can visit the Archive
+
+
+
+
+
+
Related projects
+
The idea behind 30 seconds of code has inspired some people to create similar collections in other programming languages and environments. Here are the ones we like the most:
Do you have a cool idea for a new snippet? Maybe some code you use often and is not part of our collection? Contributing to 30 seconds of code is as simple as 1,2,3,4!
Your snippet title must be unique and the same as the name of the implemented function.
+
Use the snippet description to explain what your snippet does and how it works.
+
Try to keep the snippet's code short and to the point. Use modern techniques and features.
+
Remember to provide an example of how your snippet works.
+
Your snippet should solve a real-world problem, no matter how simple.
+
Never modify README.md or any of the HTML files.
+
+
+
+
+ 2
+
+
Tag
+
Run npm run tagger from your terminal, then open the tag_database file and tag your snippet appropriately. Multitagging is also supported, just make sure the first tag you specify is on of the major tags and the one that is most relevant to the implemneted function.
+
+
+
+ 3
+
+
Test
+
You can optionally test your snippet to make our job easier. Simply run npm run tester to generate the test files for your snippet. Find the related folder for you snippet under the test directory and write some tests. Remember to run npm run tester again to make sure your tests are passing.
+
+
+
+ 4
+
+
Pull request
+
If you have done everything mentioned above, you should now have an awesome snippet to add to our collection. Simply start a pull request and follow the guidelines provided. Remember to only submit one snippet per pull request, so that we can quickly evaluate and merge your code into the collection.
+
+
+
If you need additional pointers about writing a snippet, be sure to read the complete contribution guidelines.
30 seconds of code
