Changes a function that accepts an array into a variadic function.
Given a function, return a closure that collects all inputs into an array-accepting function.
const collectInto = fn => (...args) => fn(args); +
Changes a function that accepts an array into a variadic function.
Given a function, return a closure that collects all inputs into an array-accepting function.
const collectInto = fn => (...args) => fn(args);
const Pall = collectInto(Promise.all.bind(Promise)); let p1 = Promise.resolve(1); let p2 = Promise.resolve(2); let p3 = new Promise(resolve => setTimeout(resolve, 2000, 3)); Pall(p1, p2, p3).then(console.log); -
Flip takes a function as an argument, then makes the first argument the last
Return a closure that takes variadic inputs, and splices the last argument to make it the first argument before applying the rest.
const flip = fn => (...args) => fn(args.pop(), ...args); +
Flip takes a function as an argument, then makes the first argument the last
Return a closure that takes variadic inputs, and splices the last argument to make it the first argument before applying the rest.
const flip = fn => (...args) => fn(args.pop(), ...args);
let a = { name: 'John Smith' }; let b = {}; const mergeFrom = flip(Object.assign); @@ -55,90 +55,90 @@ Promise.reso mergePerson(b); // == b b = {}; Object.assign(b, a); // == b -
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.
const pipeFunctions = (...fns) => fns.reduce((f, g) => (...args) => g(f(...args))); +
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.
const pipeFunctions = (...fns) => fns.reduce((f, g) => (...args) => g(f(...args)));
const add5 = x => x + 5; const multiply = (x, y) => x * y; const multiplyAndAdd5 = pipeFunctions(multiply, add5); multiplyAndAdd5(5, 2); // 15 -
Converts an asynchronous function to return a promise.
Use currying to return a function returning a Promise that calls the original function. Use the ...rest operator to pass in all the parameters.
In Node 8+, you can use util.promisify
const promisify = func => (...args) => +
Converts an asynchronous function to return a promise.
Use currying to return a function returning a Promise that calls the original function. Use the ...rest operator to pass in all the parameters.
In Node 8+, you can use util.promisify
const promisify = func => (...args) => new Promise((resolve, reject) => func(...args, (err, result) => (err ? reject(err) : resolve(result))) );
const delay = promisify((d, cb) => setTimeout(cb, d)); delay(2000).then(() => console.log('Hi!')); // // Promise resolves after 2s -
Takes a variadic function and returns a closure that accepts an array of arguments to map to the inputs of the function.
Use closures and the spread operator (...) to map the array of arguments to the inputs of the function.
const spreadOver = fn => argsArr => fn(...argsArr); +
Takes a variadic function and returns a closure that accepts an array of arguments to map to the inputs of the function.
Use closures and the spread operator (...) to map the array of arguments to the inputs of the function.
const spreadOver = fn => argsArr => fn(...argsArr);
const arrayMax = spreadOver(Math.max); arrayMax([1, 2, 3]); // 3 arrayMax([1, 2, 4]); // 4 -
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.
const chunk = (arr, size) => +
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.
const chunk = (arr, size) => Array.from({ length: Math.ceil(arr.length / size) }, (v, i) => arr.slice(i * size, i * size + size) );
chunk([1, 2, 3, 4, 5], 2); // [[1,2],[3,4],[5]] -
Removes falsey values from an array.
Use Array.filter() to filter out falsey values (false, null, 0, "", undefined, and NaN).
const compact = arr => arr.filter(Boolean); +
Removes falsey values from an array.
Use Array.filter() to filter out falsey values (false, null, 0, "", undefined, and NaN).
const compact = arr => arr.filter(Boolean);
compact([0, 1, false, 2, '', 3, 'a', 'e' * 23, NaN, 's', 34]); // [ 1, 2, 3, 'a', 's', 34 ] -
Counts the occurrences of a value in an array.
Use Array.reduce() to increment a counter each time you encounter the specific value inside the array.
const countOccurrences = (arr, value) => arr.reduce((a, v) => (v === value ? a + 1 : a + 0), 0); +
Counts the occurrences of a value in an array.
Use Array.reduce() to increment a counter each time you encounter the specific value inside the array.
const countOccurrences = (arr, value) => arr.reduce((a, v) => (v === value ? a + 1 : a + 0), 0);
countOccurrences([1, 1, 2, 1, 2, 3], 1); // 3 -
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.
const deepFlatten = arr => [].concat(...arr.map(v => (Array.isArray(v) ? deepFlatten(v) : v))); +
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.
const deepFlatten = arr => [].concat(...arr.map(v => (Array.isArray(v) ? deepFlatten(v) : v)));
deepFlatten([1, [2], [[3], 4], 5]); // [1,2,3,4,5] -
Returns the difference between two arrays.
Create a Set from b, then use Array.filter() on a to only keep values not contained in b.
const difference = (a, b) => { +
Returns the difference between two arrays.
Create a Set from b, then use Array.filter() on a to only keep values not contained in b.
const difference = (a, b) => { const s = new Set(b); return a.filter(x => !s.has(x)); };
difference([1, 2, 3], [1, 2, 4]); // [3] -
Filters out all values from an array for which the comparator function does not return true.
Use Array.filter() and Array.find() to find the appropriate values.
const differenceWith = (arr, val, comp) => arr.filter(a => !val.find(b => comp(a, b))); +
Filters out all values from an array for which the comparator function does not return true.
Use Array.filter() and Array.find() to find the appropriate values.
const differenceWith = (arr, val, comp) => arr.filter(a => !val.find(b => comp(a, b)));
differenceWith([1, 1.2, 1.5, 3], [1.9, 3], (a, b) => Math.round(a) == Math.round(b)); // [1, 1.2] -
Returns all the distinct values of an array.
Use ES6 Set and the ...rest operator to discard all duplicated values.
const distinctValuesOfArray = arr => [...new Set(arr)]; +
Returns all the distinct values of an array.
Use ES6 Set and the ...rest operator to discard all duplicated values.
const distinctValuesOfArray = arr => [...new Set(arr)];
distinctValuesOfArray([1, 2, 2, 3, 4, 4, 5]); // [1,2,3,4,5] -
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.
const dropElements = (arr, func) => { +
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.
const dropElements = (arr, func) => { while (arr.length > 0 && !func(arr[0])) arr = arr.slice(1); return arr; };
dropElements([1, 2, 3, 4], n => n >= 3); // [3,4] -
Returns a new array with n elements removed from the right.
Use Array.slice() to slice the remove the specified number of elements from the right.
const dropRight = (arr, n = 1) => arr.slice(0, -n); +
Returns a new array with n elements removed from the right.
Use Array.slice() to slice the remove the specified number of elements from the right.
const dropRight = (arr, n = 1) => arr.slice(0, -n);
dropRight([1, 2, 3]); // [1,2] dropRight([1, 2, 3], 2); // [1] dropRight([1, 2, 3], 42); // [] -
Returns every nth element in an array.
Use Array.filter() to create a new array that contains every nth element of a given array.
const everyNth = (arr, nth) => arr.filter((e, i) => i % nth === nth - 1); +
Returns every nth element in an array.
Use Array.filter() to create a new array that contains every nth element of a given array.
const everyNth = (arr, nth) => arr.filter((e, i) => i % nth === nth - 1);
everyNth([1, 2, 3, 4, 5, 6], 2); // [ 2, 4, 6 ] -
Filters out the non-unique values in an array.
Use Array.filter() for an array containing only the unique values.
const filterNonUnique = arr => arr.filter(i => arr.indexOf(i) === arr.lastIndexOf(i)); +
Filters out the non-unique values in an array.
Use Array.filter() for an array containing only the unique values.
const filterNonUnique = arr => arr.filter(i => arr.indexOf(i) === arr.lastIndexOf(i));
filterNonUnique([1, 2, 2, 3, 4, 4, 5]); // [1,3,5] -
Flattens an array.
Use a new array and concatenate it with the spread input array causing a shallow denesting of any contained arrays.
const flatten = arr => [].concat(...arr); +
Flattens an array.
Use a new array and concatenate it with the spread input array causing a shallow denesting of any contained arrays.
const flatten = arr => [].concat(...arr);
flatten([1, [2], 3, 4]); // [1,2,3,4] -
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 element, depth to flatten only to a depth of 1 (single flatten).
const flattenDepth = (arr, depth = 1) => +
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 element, depth to flatten only to a depth of 1 (single flatten).
const flattenDepth = (arr, depth = 1) => depth != 1 ? arr.reduce((a, v) => a.concat(Array.isArray(v) ? flattenDepth(v, depth - 1) : v), []) : arr.reduce((a, v) => a.concat(v), []);
flattenDepth([1, [2], 3, 4]); // [1,2,3,4] -
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.
const groupBy = (arr, func) => +
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.
const groupBy = (arr, func) => arr.map(typeof func === 'function' ? func : val => val[func]).reduce((acc, val, i) => { acc[val] = (acc[val] || []).concat(arr[i]); return acc; }, {});
groupBy([6.1, 4.2, 6.3], Math.floor); // {4: [4.2], 6: [6.1, 6.3]} groupBy(['one', 'two', 'three'], 'length'); // {3: ['one', 'two'], 5: ['three']} -
Returns the head of a list.
Use arr[0] to return the first element of the passed array.
const head = arr => arr[0]; +
Returns the head of a list.
Use arr[0] to return the first element of the passed array.
const head = arr => arr[0];
head([1, 2, 3]); // 1 -
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.
const initial = arr => arr.slice(0, -1); +
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.
const initial = arr => arr.slice(0, -1);
initial([1, 2, 3]); // [1,2] -
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.
const initialize2DArray = (w, h, val = null) => +
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.
const initialize2DArray = (w, h, val = null) => Array(h) .fill() .map(() => Array(w).fill(val));
initialize2DArray(2, 2, 0); // [[0,0], [0,0]] -
Initializes an array containing the numbers in the specified range where start and end are inclusive with there common difference step.
Use Array(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.
const initializeArrayWithRange = (end, start = 0, step = 1) => +
Initializes an array containing the numbers in the specified range where start and end are inclusive with there common difference step.
Use Array(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.
const initializeArrayWithRange = (end, start = 0, step = 1) => Array.from({ length: Math.ceil((end + 1 - start) / step) }).map((v, i) => i * step + start);
initializeArrayWithRange(5); // [0,1,2,3,4,5] initializeArrayWithRange(7, 3); // [3,4,5,6,7] initializeArrayWithRange(9, 0, 2); //[0,2,4,6,8] -
Initializes and fills an array with the specified values.
Use Array(n) to create an array of the desired length, fill(v) to fill it with the desired values. You can omit value to use a default value of 0.
const initializeArrayWithValues = (n, value = 0) => Array(n).fill(value); +
Initializes and fills an array with the specified values.
Use Array(n) to create an array of the desired length, fill(v) to fill it with the desired values. You can omit value to use a default value of 0.
const initializeArrayWithValues = (n, value = 0) => Array(n).fill(value);
initializeArrayWithValues(5, 2); // [2,2,2,2,2] -
Returns a list of elements that exist in both arrays.
Create a Set from b, then use Array.filter() on a to only keep values contained in b.
const intersection = (a, b) => { +
Returns a list of elements that exist in both arrays.
Create a Set from b, then use Array.filter() on a to only keep values contained in b.
const intersection = (a, b) => { const s = new Set(b); return a.filter(x => s.has(x)); };
intersection([1, 2, 3], [4, 3, 2]); // [2,3] -
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.
const isSorted = arr => { +
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.
const isSorted = arr => { const direction = arr[0] > arr[1] ? -1 : 1; for (let [i, val] of arr.entries()) if (i === arr.length - 1) return direction; @@ -148,7 +148,7 @@ Object.assig isSorted([0, 1, 2, 2]); // 1 isSorted([4, 3, 2]); // -1 isSorted([4, 3, 5]); // 0 -
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) => +
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 @@ -160,29 +160,29 @@ Object.assig join(['pen', 'pineapple', 'apple', 'pen'], ',', '&'); //"pen,pineapple,apple&pen" join(['pen', 'pineapple', 'apple', 'pen'], ','); //"pen,pineapple,apple,pen" join(['pen', 'pineapple', 'apple', 'pen']); //"pen,pineapple,apple,pen" -
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.
const last = arr => arr[arr.length - 1]; +
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.
const last = arr => arr[arr.length - 1];
last([1, 2, 3]); // 3 -
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).
const mapObject = (arr, fn) => +
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).
const mapObject = (arr, fn) => (a => ( (a = [arr, arr.map(fn)]), a[0].reduce((acc, val, ind) => ((acc[val] = a[1][ind]), acc), {}) ))();
const squareIt = arr => mapObject(arr, a => a * a); squareIt([1, 2, 3]); // { 1: 1, 2: 4, 3: 9 } -
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.
const maxN = (arr, n = 1) => [...arr].sort((a, b) => b - a).slice(0, n); +
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.
const maxN = (arr, n = 1) => [...arr].sort((a, b) => b - a).slice(0, n);
maxN([1, 2, 3]); // [3] maxN([1, 2, 3], 2); // [3,2] maxN([1, 2, 3], 4); // [3,2,1] -
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.
const minN = (arr, n = 1) => [...arr].sort((a, b) => a - b).slice(0, n); +
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.
const minN = (arr, n = 1) => [...arr].sort((a, b) => a - b).slice(0, n);
minN([1, 2, 3]); // [1] minN([1, 2, 3], 2); // [1,2] minN([1, 2, 3], 4); // [1,2,3] -
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.
const nthElement = (arr, n = 0) => (n > 0 ? arr.slice(n, n + 1) : arr.slice(n))[0]; +
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.
const nthElement = (arr, n = 0) => (n > 0 ? arr.slice(n, n + 1) : arr.slice(n))[0];
nthElement(['a', 'b', 'c'], 1); // 'b' nthElement(['a', 'b', 'b'], -3); // 'a' -
Picks the key-value pairs corresponding to the given keys from an object.
Use Array.reduce() to convert the filtered/picked keys back to an object with the corresponding key-value pair if the key exists in the obj.
const pick = (obj, arr) => +
Picks the key-value pairs corresponding to the given keys from an object.
Use Array.reduce() to convert the filtered/picked keys back to an object with the corresponding key-value pair if the key exists in the obj.
const pick = (obj, arr) => arr.reduce((acc, curr) => (curr in obj && (acc[curr] = obj[curr]), acc), {});
pick({ a: 1, b: '2', c: 3 }, ['a', 'c']); // { 'a': 1, 'c': 3 } -
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)
const pull = (arr, ...args) => { +
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)
const pull = (arr, ...args) => { let argState = Array.isArray(args[0]) ? args[0] : args; let pulled = arr.filter((v, i) => !argState.includes(v)); arr.length = 0; @@ -195,7 +195,7 @@ console.log< let myArray2 = ['a', 'b', 'c', 'a', 'b', 'c']; pull(myArray2, ['a', 'c']); console.log(myArray2); // [ 'b', 'b' ] -
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
const pullAtIndex = (arr, pullArr) => { +
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
const pullAtIndex = (arr, pullArr) => { let removed = []; let pulled = arr .map((v, i) => (pullArr.includes(i) ? removed.push(v) : v)) @@ -209,7 +209,7 @@ console.log< console.log(myArray); // [ 'a', 'c' ] console.log(pulled); // [ 'b', 'd' ] -
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
const pullAtValue = (arr, pullArr) => { +
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
const pullAtValue = (arr, pullArr) => { let removed = [], pushToRemove = arr.forEach((v, i) => (pullArr.includes(v) ? removed.push(v) : v)), mutateTo = arr.filter((v, i) => !pullArr.includes(v)); @@ -221,7 +221,7 @@ console.log< let pulled = pullAtValue(myArray, ['b', 'd']); console.log(myArray); // [ 'a', 'c' ] console.log(pulled); // [ 'b', 'd' ] -
QuickSort an Array (ascending sort by default).
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.
const quickSort = ([n, ...nums], desc) => +
QuickSort an Array (ascending sort by default).
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.
const quickSort = ([n, ...nums], desc) => isNaN(n) ? [] : [ @@ -231,7 +231,7 @@ console.log< ];
quickSort([4, 1, 3, 2]); // [1,2,3,4] quickSort([4, 1, 3, 2], true); // [4,3,2,1] -
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.
const reducedFilter = (data, keys, fn) => +
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.
const reducedFilter = (data, keys, fn) => data.filter(fn).map(el => keys.reduce((acc, key) => { acc[key] = el[key]; @@ -252,7 +252,7 @@ console.log< ]; reducedFilter(data, ['id', 'name'], item => item.age > 24); // [{ id: 2, name: 'mike'}] -
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).
const remove = (arr, func) => +
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).
const remove = (arr, func) => Array.isArray(arr) ? arr.filter(func).reduce((acc, val) => { arr.splice(arr.indexOf(val), 1); @@ -260,9 +260,9 @@ console.log< }, []) : [];
remove([1, 2, 3, 4], n => n % 2 == 0); // [2, 4] -
Returns a random element from an 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.
const sample = arr => arr[Math.floor(Math.random() * arr.length)]; +
Returns a random element from an 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.
const sample = arr => arr[Math.floor(Math.random() * arr.length)];
sample([3, 7, 9, 11]); // 9 -
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.
const sampleSize = ([...arr], n = 1) => { +
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.
const sampleSize = ([...arr], n = 1) => { let m = arr.length; while (m) { const i = Math.floor(Math.random() * m--); @@ -272,7 +272,7 @@ console.log< };
sampleSize([1, 2, 3], 2); // [3,1] sampleSize([1, 2, 3], 4); // [2,3,1] -
Randomizes the order of the values of an array, returning a new array.
Uses the Fisher-Yates algorithm to reorder the elements of the array, based on the Lodash implementation, but as a pure function.
const shuffle = ([...arr]) => { +
Randomizes the order of the values of an array, returning a new array.
Uses the Fisher-Yates algorithm to reorder the elements of the array, based on the Lodash implementation, but as a pure function.
const shuffle = ([...arr]) => { let m = arr.length; while (m) { const i = Math.floor(Math.random() * m--); @@ -283,35 +283,35 @@ console.log<
const foo = [1, 2, 3]; shuffle(foo); // [2,3,1] console.log(foo); // [1,2,3] -
Returns an array of elements that appear in both arrays.
Use filter() to remove values that are not part of values, determined using includes().
const similarity = (arr, values) => arr.filter(v => values.includes(v)); +
Returns an array of elements that appear in both arrays.
Use filter() to remove values that are not part of values, determined using includes().
const similarity = (arr, values) => arr.filter(v => values.includes(v));
similarity([1, 2, 3], [1, 2, 4]); // [1,2] -
Returns the lowest 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.findIndex() to find the appropriate index where the element should be inserted.
const sortedIndex = (arr, n) => { +
Returns the lowest 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.findIndex() to find the appropriate index where the element should be inserted.
const sortedIndex = (arr, n) => { const isDescending = arr[0] > arr[arr.length - 1]; const index = arr.findIndex(el => (isDescending ? n >= el : n <= el)); return index === -1 ? arr.length : index; };
sortedIndex([5, 3, 2, 1], 4); // 1 sortedIndex([30, 50], 40); // 1 -
Returns the symmetric difference between two arrays.
Create a Set from each array, then use Array.filter() on each of them to only keep values not contained in the other.
const symmetricDifference = (a, b) => { +
Returns the symmetric difference between two arrays.
Create a Set from each array, then use Array.filter() on each of them to only keep values not contained in the other.
const symmetricDifference = (a, b) => { const sA = new Set(a), sB = new Set(b); return [...a.filter(x => !sB.has(x)), ...b.filter(x => !sA.has(x))]; };
symmetricDifference([1, 2, 3], [1, 2, 4]); // [3,4] -
Returns all elements in an array except for the first one.
Return arr.slice(1) if the array's length is more than 1, otherwise, return the whole array.
const tail = arr => (arr.length > 1 ? arr.slice(1) : arr); +
Returns all elements in an array except for the first one.
Return arr.slice(1) if the array's length is more than 1, otherwise, return the whole array.
const tail = arr => (arr.length > 1 ? arr.slice(1) : arr);
tail([1, 2, 3]); // [2,3] tail([1]); // [1] -
Returns an array with n elements removed from the beginning.
Use Array.slice() to create a slice of the array with n elements taken from the beginning.
const take = (arr, n = 1) => arr.slice(0, n); +
Returns an array with n elements removed from the beginning.
Use Array.slice() to create a slice of the array with n elements taken from the beginning.
const take = (arr, n = 1) => arr.slice(0, n);
take([1, 2, 3], 5); // [1, 2, 3] take([1, 2, 3], 0); // [] -
Returns an array with n elements removed from the end.
Use Array.slice() to create a slice of the array with n elements taken from the end.
const takeRight = (arr, n = 1) => arr.slice(arr.length - n, arr.length); +
Returns an array with n elements removed from the end.
Use Array.slice() to create a slice of the array with n elements taken from the end.
const takeRight = (arr, n = 1) => arr.slice(arr.length - n, arr.length);
takeRight([1, 2, 3], 2); // [ 2, 3 ] takeRight([1, 2, 3]); // [3] -
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.
const union = (a, b) => Array.from(new Set([...a, ...b])); +
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.
const union = (a, b) => Array.from(new Set([...a, ...b]));
union([1, 2, 3], [4, 3, 2]); // [1,2,3,4] -
Filters out the elements of an array, that have one of the specified values.
Use Array.filter() to create an array excluding(using !Array.includes()) all given values.
(For a snippet that mutates the original array see pull)
const without = (arr, ...args) => arr.filter(v => !args.includes(v)); +
Filters out the elements of an array, that have one of the specified values.
Use Array.filter() to create an array excluding(using !Array.includes()) all given values.
(For a snippet that mutates the original array see pull)
const without = (arr, ...args) => arr.filter(v => !args.includes(v));
without([2, 1, 2, 3], 1, 2); // [3] -
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.
const zip = (...arrays) => { +
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.
const zip = (...arrays) => { const maxLength = Math.max(...arrays.map(x => x.length)); return Array.from({ length: maxLength }).map((_, i) => { return Array.from({ length: arrays.length }, (_, k) => arrays[k][i]); @@ -319,18 +319,18 @@ console.log< };
zip(['a', 'b'], [1, 2], [true, false]); // [['a', 1, true], ['b', 2, false]] zip(['a'], [1, 2], [true, false]); // [['a', 1, true], [undefined, 2, false]] -
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().
const zipObject = (props, values) => +
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().
const zipObject = (props, values) => props.reduce((obj, prop, index) => ((obj[prop] = values[index]), obj), {});
zipObject(['a', 'b', 'c'], [1, 2]); // {a: 1, b: 2, c: undefined} zipObject(['a', 'b'], [1, 2, 3]); // {a: 1, b: 2} -
Converts the given array elements into <li> tags and appends them to the list of the given id.
Use Array.map() and document.querySelector() to create a list of html tags.
const arrayToHtmlList = (arr, listID) => +
Converts the given array elements into <li> tags and appends them to the list of the given id.
Use Array.map() and document.querySelector() to create a list of html tags.
const arrayToHtmlList = (arr, listID) => arr.map(item => (document.querySelector('#' + listID).innerHTML += `<li>${item}</li>`));
arrayToHtmlList(['item 1', 'item 2'], 'myListID'); -
Returns true if the bottom of the page is visible, false otherwise.
Use scrollY, scrollHeight and clientHeight to determine if the bottom of the page is visible.
const bottomVisible = () => +
Returns true if the bottom of the page is visible, false otherwise.
Use scrollY, scrollHeight and clientHeight to determine if the bottom of the page is visible.
const bottomVisible = () => document.documentElement.clientHeight + window.scrollY >= (document.documentElement.scrollHeight || document.documentElement.clientHeight);
bottomVisible(); // true -
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).
const copyToClipboard = str => { +
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).
const copyToClipboard = str => { const el = document.createElement('textarea'); el.value = str; el.setAttribute('readonly', ''); @@ -348,15 +348,15 @@ console.log< } };
copyToClipboard('Lorem ipsum'); // 'Lorem ipsum' copied to clipboard. -
Returns the current URL.
Use window.location.href to get current URL.
const currentURL = () => window.location.href; +
Returns the current URL.
Use window.location.href to get current URL.
const currentURL = () => window.location.href;
currentURL(); // 'https://google.com' -
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.
const 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.
const detectDeviceType = () => /Android|webOS|iPhone|iPad|iPod|BlackBerry|IEMobile|Opera Mini/i.test(navigator.userAgent) ? 'Mobile' : 'Desktop';
detectDeviceType(); // "Mobile" detectDeviceType(); // "Desktop" -
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.
const elementIsVisibleInViewport = (el, partiallyVisible = false) => { +
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.
const elementIsVisibleInViewport = (el, partiallyVisible = false) => { const { top, left, bottom, right } = el.getBoundingClientRect(); const { innerHeight, innerWidth } = window; return partiallyVisible @@ -367,21 +367,21 @@ console.log<
// 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) -
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.
const getScrollPosition = (el = window) => ({ +
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.
const getScrollPosition = (el = window) => ({ x: el.pageXOffset !== undefined ? el.pageXOffset : el.scrollLeft, y: el.pageYOffset !== undefined ? el.pageYOffset : el.scrollTop });
getScrollPosition(); // {x: 0, y: 200} -
Returns the value of a CSS rule for the specified element.
Use Window.getComputedStyle() to get the value of the CSS rule for the specified element.
const getStyle = (el, ruleName) => getComputedStyle(el)[ruleName]; +
Returns the value of a CSS rule for the specified element.
Use Window.getComputedStyle() to get the value of the CSS rule for the specified element.
const getStyle = (el, ruleName) => getComputedStyle(el)[ruleName];
getStyle(document.querySelector('p'), 'font-size'); // '16px' -
Returns true if the element has the specified class, false otherwise.
Use element.classList.contains() to check if the element has the specified class.
const hasClass = (el, className) => el.classList.contains(className); +
Returns true if the element has the specified class, false otherwise.
Use element.classList.contains() to check if the element has the specified class.
const hasClass = (el, className) => el.classList.contains(className);
hasClass(document.querySelector('p.special'), 'special'); // true -
Hides all the elements specified.
Use the spread operator (...) and Array.forEach() to apply display: none to each element specified.
const hide = (...el) => [...el].forEach(e => (e.style.display = 'none')); +
Hides all the elements specified.
Use the spread operator (...) and Array.forEach() to apply display: none to each element specified.
const hide = (...el) => [...el].forEach(e => (e.style.display = 'none'));
hide(document.querySelectorAll('img')); // Hides all <img> elements on the page -
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.
const 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.
const httpsRedirect = () => { if (location.protocol !== 'https:') location.replace('https://' + location.href.split('//')[1]); }; -
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.
const onUserInputChange = callback => { +
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.
const onUserInputChange = callback => { let type = 'mouse', lastTime = 0; const mousemoveHandler = () => { @@ -398,10 +398,10 @@ console.log<
onUserInputChange(type => { console.log('The user is now using', type, 'as an input method.'); }); -
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).
const redirect = (url, asLink = true) => +
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).
const redirect = (url, asLink = true) => asLink ? (window.location.href = url) : window.location.replace(url);
redirect('https://google.com'); -
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.
const runAsync = fn => { +
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.
const runAsync = fn => { const blob = `var fn = ${fn.toString()}; postMessage(fn());`; const worker = new Worker( URL.createObjectURL(new Blob([blob]), { @@ -436,7 +436,7 @@ console.log< runAsync(() => 10 ** 3).then(console.log); // 1000 let outsideVariable = 50; runAsync(() => typeof outsideVariable).then(console.log); // 'undefined' -
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.
const 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.
const scrollToTop = () => { const c = document.documentElement.scrollTop || document.body.scrollTop; if (c > 0) { window.requestAnimationFrame(scrollToTop); @@ -444,32 +444,32 @@ console.log< } };
scrollToTop(); -
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 value.
const setStyle = (el, ruleName, value) => (el.style[ruleName] = value); +
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 value.
const setStyle = (el, ruleName, value) => (el.style[ruleName] = value);
setStyle(document.querySelector('p'), 'font-size', '20px'); // The first <p> element on the page will have a font-size of 20px -
Shows all the elements specified.
Use the spread operator (...) and Array.forEach() to clear the display property for each element specified.
const show = (...el) => [...el].forEach(e => (e.style.display = '')); +
Shows all the elements specified.
Use the spread operator (...) and Array.forEach() to clear the display property for each element specified.
const show = (...el) => [...el].forEach(e => (e.style.display = ''));
show(document.querySelectorAll('img')); // Shows all <img> elements on the page -
Performs speech synthesis (experimental).
Use SpeechSynthesisUtterance.voice and window.speechSynthesis.getVoices() to convert a message to speech. Use window.speechSynthesis.speak() to play the message.
Learn more about the SpeechSynthesisUtterance interface of the Web Speech API.
const speechSynthesis = message => { +
Performs speech synthesis (experimental).
Use SpeechSynthesisUtterance.voice and window.speechSynthesis.getVoices() to convert a message to speech. Use window.speechSynthesis.speak() to play the message.
Learn more about the SpeechSynthesisUtterance interface of the Web Speech API.
const speechSynthesis = message => { const msg = new SpeechSynthesisUtterance(message); msg.voice = window.speechSynthesis.getVoices()[0]; window.speechSynthesis.speak(msg); };
speechSynthesis('Hello, World'); // // plays the message -
Toggle a class for an element.
Use element.classList.toggle() to toggle the specified class for the element.
const toggleClass = (el, className) => el.classList.toggle(className); +
Toggle a class for an element.
Use element.classList.toggle() to toggle the specified class for the element.
const toggleClass = (el, className) => el.classList.toggle(className);
toggleClass(document.querySelector('p.special'), 'special'); // The paragraph will not have the 'special' class anymore -
Generates a UUID in a browser.
Use crypto API to generate a UUID, compliant with RFC4122 version 4.
const UUIDGeneratorBrowser = () => +
Generates a UUID in a browser.
Use crypto API to generate a UUID, compliant with RFC4122 version 4.
const UUIDGeneratorBrowser = () => ([1e7] + -1e3 + -4e3 + -8e3 + -1e11).replace(/[018]/g, c => (c ^ (crypto.getRandomValues(new Uint8Array(1))[0] & (15 >> (c / 4)))).toString(16) );
UUIDGeneratorBrowser(); // '7982fcfe-5721-4632-bede-6000885be57d' -
Returns the difference (in days) between two dates.
Calculate the difference (in days) between two Date objects.
const getDaysDiffBetweenDates = (dateInitial, dateFinal) => +
Returns the difference (in days) between two dates.
Calculate the difference (in days) between two Date objects.
const getDaysDiffBetweenDates = (dateInitial, dateFinal) => (dateFinal - dateInitial) / (1000 * 3600 * 24);
getDaysDiffBetweenDates(new Date('2017-12-13'), new Date('2017-12-22')); // 9 -
Converts a JSON object to a date.
Use Date(), to convert dates in JSON format to readable format (dd/mm/yyyy).
const JSONToDate = arr => { +
Converts a JSON object to a date.
Use Date(), to convert dates in JSON format to readable format (dd/mm/yyyy).
const JSONToDate = arr => { const dt = new Date(parseInt(arr.toString().substr(6))); return `${dt.getDate()}/${dt.getMonth() + 1}/${dt.getFullYear()}`; };
JSONToDate(/Date(1489525200000)/); // "14/3/2017" -
Converts a date from American format to English format.
Use Date.toISOString(), split('T') and replace() to convert a date from American format to the English format. Throws an error if the passed time cannot be converted to a date.
const toEnglishDate = time => { +
Converts a date from American format to English format.
Use Date.toISOString(), split('T') and replace() to convert a date from American format to the English format. Throws an error if the passed time cannot be converted to a date.
const toEnglishDate = time => { try { return new Date(time) .toISOString() @@ -478,9 +478,9 @@ console.log< } catch (e) {} };
toEnglishDate('09/21/2010'); // '21/09/2010' -
Results in a string representation of tomorrow's date. Use new Date() to get today's date, adding 86400000 of seconds to it(24 hours), using toISOString to convert Date object to string.
const tomorrow = () => new Date(new Date().getTime() + 86400000).toISOString().split('T')[0]; +
Results in a string representation of tomorrow's date. Use new Date() to get today's date, adding 86400000 of seconds to it(24 hours), using toISOString to convert Date object to string.
const tomorrow = () => new Date(new Date().getTime() + 86400000).toISOString().split('T')[0];
tomorrow(); // 2017-12-27 (if current date is 2017-12-26) -
Chains asynchronous functions.
Loop through an array of functions containing asynchronous events, calling next when each asynchronous event has completed.
const chainAsync = fns => { +
Chains asynchronous functions.
Loop through an array of functions containing asynchronous events, calling next when each asynchronous event has completed.
const chainAsync = fns => { let curr = 0; const next = () => fns[curr++](next); next(); @@ -498,16 +498,16 @@ console.log< console.log('2 seconds'); } ]); -
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.
const compose = (...fns) => fns.reduce((f, g) => (...args) => f(g(...args))); +
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.
const compose = (...fns) => fns.reduce((f, g) => (...args) => f(g(...args)));
const add5 = x => x + 5; const multiply = (x, y) => x * y; const multiplyAndAdd5 = compose(add5, multiply); multiplyAndAdd5(5, 2); // 15 -
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.
const curry = (fn, arity = fn.length, ...args) => +
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.
const curry = (fn, arity = fn.length, ...args) => arity <= args.length ? fn(...args) : curry.bind(null, fn, arity, ...args);
curry(Math.pow)(2)(10); // 1024 curry(Math.min, 3)(10)(50)(2); // 2 -
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.
const defer = (fn, ...args) => setTimeout(fn, 1, ...args); +
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.
const defer = (fn, ...args) => setTimeout(fn, 1, ...args);
// Example A: defer(console.log, 'a'), console.log('b'); // logs 'b' then 'a' @@ -515,9 +515,9 @@ console.log< document.querySelector('#someElement').innerHTML = 'Hello'; longRunningFunction(); // the browser will not update the HTML until this has finished defer(longRunningFunction); // the browser will update the HTML then run the function -
Logs the name of a function.
Use console.debug() and the name property of the passed method to log the method's name to the debug channel of the console.
const functionName = fn => (console.debug(fn.name), fn); +
Logs the name of a function.
Use console.debug() and the name property of the passed method to log the method's name to the debug channel of the console.
const functionName = fn => (console.debug(fn.name), fn);
functionName(Math.max); // max (logged in debug channel of console) -
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.
const memoize = fn => { +
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.
const memoize = fn => { const cache = new Map(); const cached = function(val) { return cache.has(val) ? cache.get(val) : cache.set(val, fn.call(this, val)) && cache.get(val); @@ -530,7 +530,7 @@ document.que anagramsCached('javascript'); // takes a long time anagramsCached('javascript'); // returns virtually instantly since it's now cached console.log(anagramsCached.cache); // Map -
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.
const once = fn => { +
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.
const once = fn => { let called = false; return function(...args) { if (called) return; @@ -542,36 +542,36 @@ console.log< console.log(this, event); // document.body, MouseEvent }; document.body.addEventListener('click', once(startApp)); // only runs `startApp` once upon click -
Runs an array of promises in series.
Use Array.reduce() to create a promise chain, where each promise returns the next promise when resolved.
const runPromisesInSeries = ps => ps.reduce((p, next) => p.then(next), Promise.resolve()); +
Runs an array of promises in series.
Use Array.reduce() to create a promise chain, where each promise returns the next promise when resolved.
const runPromisesInSeries = ps => ps.reduce((p, next) => p.then(next), Promise.resolve());
const delay = d => new Promise(r => setTimeout(r, d)); runPromisesInSeries([() => delay(1000), () => delay(2000)]); // //executes each promise sequentially, taking a total of 3 seconds to complete -
Delays the execution of an asynchronous function.
Delay executing part of an async function, by putting it to sleep, returning a Promise.
const sleep = ms => new Promise(resolve => setTimeout(resolve, ms)); +
Delays the execution of an asynchronous function.
Delay executing part of an async function, by putting it to sleep, returning a Promise.
const sleep = ms => new Promise(resolve => setTimeout(resolve, ms));
async function sleepyWork() { console.log("I'm going to sleep for 1 second."); await sleep(1000); console.log('I woke up after 1 second.'); } -
Negates a predicate function.
Take a predicate function and apply not to it with its arguments.
const negate = func => (...args) => !func(...args); +
Negates a predicate function.
Take a predicate function and apply not to it with its arguments.
const negate = func => (...args) => !func(...args);
filter([1, 2, 3, 4, 5, 6], negate(isEven)); // [1, 3, 5] negate(isOdd)(1); // false -
Returns the average of an of two or more numbers/arrays.
Use Array.reduce() to add each value to an accumulator, initialized with a value of 0, divide by the length of the array.
const average = (...arr) => { +
Returns the average of an of two or more numbers/arrays.
Use Array.reduce() to add each value to an accumulator, initialized with a value of 0, divide by the length of the array.
const average = (...arr) => { const nums = [].concat(...arr); return nums.reduce((acc, val) => acc + val, 0) / nums.length; };
average([1, 2, 3]); // 2 average(1, 2, 3); // 2 -
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.
const clampNumber = (num, a, b) => Math.max(Math.min(num, Math.max(a, b)), Math.min(a, b)); +
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.
const clampNumber = (num, a, b) => Math.max(Math.min(num, Math.max(a, b)), Math.min(a, b));
clampNumber(2, 3, 5); // 3 clampNumber(1, -1, -5); // -1 clampNumber(3, 2, 4); // 3 -
Applies the Collatz algorithm.
If n is even, return n/2. Otherwise, return 3n+1.
const collatz = n => (n % 2 == 0 ? n / 2 : 3 * n + 1); +
Applies the Collatz algorithm.
If n is even, return n/2. Otherwise, return 3n+1.
const collatz = n => (n % 2 == 0 ? n / 2 : 3 * n + 1);
collatz(8); // 4 collatz(5); // 16 -
Converts a number to an array of digits.
Convert the number to a string, using spread operators in ES6([...string]) build an array. Use Array.map() and parseInt() to transform each value to an integer.
const digitize = n => [...('' + n)].map(i => parseInt(i)); +
Converts a number to an array of digits.
Convert the number to a string, using spread operators in ES6([...string]) build an array. Use Array.map() and parseInt() to transform each value to an integer.
const digitize = n => [...('' + n)].map(i => parseInt(i));
digitize(123); // [1, 2, 3] -
Returns the distance between two points.
Use Math.hypot() to calculate the Euclidean distance between two points.
const distance = (x0, y0, x1, y1) => Math.hypot(x1 - x0, y1 - y0); +
Returns the distance between two points.
Use Math.hypot() to calculate the Euclidean distance between two points.
const distance = (x0, y0, x1, y1) => Math.hypot(x1 - x0, y1 - y0);
distance(1, 1, 2, 3); // 2.23606797749979 -
Computes the new ratings between two opponents using the Elo rating system. It takes an array of two pre-ratings and returns an array containing two post-ratings. The winner's rating is the first element of the array.
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. Omit the second argument to use the default K-factor of 32, or supply a custom K-factor value.
const elo = ([a, b], kFactor = 32) => { +
Computes the new ratings between two opponents using the Elo rating system. It takes an array of two pre-ratings and returns an array containing two post-ratings. The winner's rating is the first element of the array.
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. Omit the second argument to use the default K-factor of 32, or supply a custom K-factor value.
const elo = ([a, b], kFactor = 32) => { const expectedScore = (self, opponent) => 1 / (1 + 10 ** ((opponent - self) / 400)); const newRating = (rating, i) => rating + kFactor * (i - expectedScore(i ? a : b, i ? b : a)); return [newRating(a, 1), newRating(b, 0)]; @@ -580,14 +580,14 @@ document.bodyelo([1000, 2000]); // [1031.8991261061358, 1968.1008738938642] elo([1500, 1000]); // [1501.7036868864648, 998.2963131135352] elo([1200, 1200], 64); // [1232, 1168] -
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.
const factorial = n => +
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.
const factorial = n => n < 0 ? (() => { throw new TypeError('Negative numbers are not allowed!'); })() : n <= 1 ? 1 : n * factorial(n - 1);
factorial(6); // 720 -
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.
const factors = (num, primes = false) => { +
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.
const factors = (num, primes = false) => { const isPrime = num => { const boundary = Math.floor(Math.sqrt(num)); for (var i = 2; i <= boundary; i++) if (num % i === 0) return false; @@ -610,16 +610,16 @@ document.bodyfactors(12, true); // [2,3] factors(-12); // [2, -2, 3, -3, 4, -4, 6, -6, 12, -12] factors(-12, true); // [2,3] -
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.
const fibonacci = n => +
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.
const fibonacci = n => Array.from({ length: n }).reduce( (acc, val, i) => acc.concat(i > 1 ? acc[i - 1] + acc[i - 2] : i), [] );
fibonacci(6); // [0, 1, 1, 2, 3, 5] -
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.
const fibonacciCountUntilNum = num => +
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.
const fibonacciCountUntilNum = num => Math.ceil(Math.log(num * Math.sqrt(5) + 1 / 2) / Math.log((Math.sqrt(5) + 1) / 2));
fibonacciCountUntilNum(10); // 7 -
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.
const fibonacciUntilNum = num => { +
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.
const fibonacciUntilNum = 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), @@ -627,13 +627,13 @@ document.bodyShow examplesfibonacciUntilNum(10); // [ 0, 1, 1, 2, 3, 5, 8 ] -
Calculates the greatest common divisor between two or more numbers/arrays.
The helperGcdfunction 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.
const gcd = (...arr) => { +
Calculates the greatest common divisor between two or more numbers/arrays.
The helperGcdfunction 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.
const gcd = (...arr) => { let data = [].concat(...arr); const helperGcd = (x, y) => (!y ? x : gcd(y, x % y)); return data.reduce((a, b) => helperGcd(a, b)); };
gcd(8, 36); // 4 -
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.
const geometricProgression = (end, start = 1, step = 2) => +
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.
const geometricProgression = (end, start = 1, step = 2) => Array.from({ length: Math.floor(Math.log(end / start) / Math.log(step)) + 1 }).map( (v, i) => start * step ** i ); @@ -641,9 +641,9 @@ document.bodygeometricProgression(256, 3); //[3, 6, 12, 24, 48, 96, 192] geometricProgression(256, 1, 4); //[1, 4, 16, 64, 256] geometricProgression(256, 2, 1); //Gives error -
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).
const hammingDistance = (num1, num2) => ((num1 ^ num2).toString(2).match(/1/g) || '').length; +
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).
const hammingDistance = (num1, num2) => ((num1 ^ num2).toString(2).match(/1/g) || '').length;
hammingDistance(2, 3); // 1 -
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.
const howManyTimes = (num, divisor) => { +
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.
const howManyTimes = (num, divisor) => { if (divisor === 1 || divisor === -1) return Infinity; if (divisor === 0) return 0; let i = 0; @@ -660,7 +660,7 @@ document.bodyhowManyTimes(100, 0); //0 howManyTimes(100, 1); //Infinity howManyTimes(100, -1); //Infinity -
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.
const inRange = (n, start, end = null) => { +
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.
const inRange = (n, start, end = null) => { if (end && start > end) end = [start, (start = end)][0]; return end == null ? n >= 0 && n < start : n >= start && n < end; }; @@ -668,44 +668,44 @@ document.bodyinRange(3, 4); // true inRange(2, 3, 5); // false inrange(3, 2); // false -
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.
const isArmstrongNumber = digits => +
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.
const isArmstrongNumber = digits => (arr => arr.reduce((a, d) => a + parseInt(d) ** arr.length, 0) == digits)( (digits + '').split('') );
isArmstrongNumber(1634); // true isArmstrongNumber(371); // true isArmstrongNumber(56); // false -
Checks if the first numeric argument is divisible by the second one.
Use the modulo operator (%) to check if the remainder is equal to 0.
const isDivisible = (dividend, divisor) => dividend % divisor === 0; +
Checks if the first numeric argument is divisible by the second one.
Use the modulo operator (%) to check if the remainder is equal to 0.
const isDivisible = (dividend, divisor) => dividend % divisor === 0;
isDivisible(6, 3); // true -
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.
const isEven = num => num % 2 === 0; +
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.
const isEven = num => num % 2 === 0;
isEven(3); // false -
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.
const isPrime = num => { +
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.
const isPrime = num => { const boundary = Math.floor(Math.sqrt(num)); for (var i = 2; i <= boundary; i++) if (num % i == 0) return false; return num >= 2; };
isPrime(11); // true isPrime(12); // false -
Returns the least common multiple of two or more numbers/arrays.
Use the greatest common divisor (GCD) formula and Math.abs() to determine the least common multiple. The GCD formula uses recursion.
const lcm = (...arr) => { +
Returns the least common multiple of two or more numbers/arrays.
Use the greatest common divisor (GCD) formula and Math.abs() to determine the least common multiple. The GCD formula uses recursion.
const lcm = (...arr) => { const gcd = (x, y) => (!y ? x : gcd(y, x % y)); const _lcm = (x, y) => x * y / gcd(x, y); return [].concat(...arr).reduce((a, b) => _lcm(a, b)); };
lcm(12, 7); // 84 lcm([1, 3, 4], 5); // 60 -
Returns the median of an array of numbers.
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.
const median = arr => { +
Returns the median of an array of numbers.
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.
const median = arr => { const mid = Math.floor(arr.length / 2), nums = [...arr].sort((a, b) => a - b); return arr.length % 2 !== 0 ? nums[mid] : (nums[mid - 1] + nums[mid]) / 2; };
median([5, 6, 50, 1, -5]); // 5 median([0, 10, -2, 7]); // 3.5 -
Uses the percentile formula to calculate how many numbers in the given array are less or equal to the given value.
Use Array.reduce() to calculate how many numbers are below the value and how many are the same value and apply the percentile formula.
const percentile = (arr, val) => +
Uses the percentile formula to calculate how many numbers in the given array are less or equal to the given value.
Use Array.reduce() to calculate how many numbers are below the value and how many are the same value and apply the percentile formula.
const percentile = (arr, val) => 100 * arr.reduce((acc, v) => acc + (v < val ? 1 : 0) + (v === val ? 0.5 : 0), 0) / arr.length;
percentile([1, 2, 3, 4, 5, 6, 7, 8, 9, 10], 6); // 55 -
Returns the powerset of a given array of numbers.
Use Array.reduce() combined with Array.map() to iterate over elements and combine into an array containing all combinations.
const powerset = arr => arr.reduce((a, v) => a.concat(a.map(r => [v].concat(r))), [[]]); +
Returns the powerset of a given array of numbers.
Use Array.reduce() combined with Array.map() to iterate over elements and combine into an array containing all combinations.
const powerset = arr => arr.reduce((a, v) => a.concat(a.map(r => [v].concat(r))), [[]]);
powerset([1, 2]); // [[], [1], [2], [2,1]] -
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.
const primes = num => { +
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.
const primes = 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); @@ -713,13 +713,13 @@ document.bodyreturn arr; };
primes(10); // [2,3,5,7] -
Returns a random integer in the specified range.
Use Math.random() to generate a random number and map it to the desired range, using Math.floor() to make it an integer.
const randomIntegerInRange = (min, max) => Math.floor(Math.random() * (max - min + 1)) + min; +
Returns a random integer in the specified range.
Use Math.random() to generate a random number and map it to the desired range, using Math.floor() to make it an integer.
const randomIntegerInRange = (min, max) => Math.floor(Math.random() * (max - min + 1)) + min;
randomIntegerInRange(0, 5); // 2 -
Returns a random number in the specified range.
Use Math.random() to generate a random value, map it to the desired range using multiplication.
const randomNumberInRange = (min, max) => Math.random() * (max - min) + min; +
Returns a random number in the specified range.
Use Math.random() to generate a random value, map it to the desired range using multiplication.
const randomNumberInRange = (min, max) => Math.random() * (max - min) + min;
randomNumberInRange(2, 10); // 6.0211363285087005 -
Rounds a number to a specified amount of digits.
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.
const round = (n, decimals = 0) => Number(`${Math.round(`${n}e${decimals}`)}e-${decimals}`); +
Rounds a number to a specified amount of digits.
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.
const round = (n, decimals = 0) => Number(`${Math.round(`${n}e${decimals}`)}e-${decimals}`);
round(1.005, 2); // 1.01 -
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.
const solveRPN = rpn => { +
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.
const solveRPN = rpn => { const OPERATORS = { '*': (a, b) => a * b, '+': (a, b) => a + b, @@ -752,7 +752,7 @@ document.bodysolveRPN('2 4 / 5 6 - *'); //-0.5 solveRPN('2 3 ^'); //8 solveRPN('2 3 ^'); //8 -
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.
const standardDeviation = (arr, usePopulation = false) => { +
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.
const standardDeviation = (arr, usePopulation = false) => { const mean = arr.reduce((acc, val) => acc + val, 0) / arr.length; return Math.sqrt( arr.reduce((acc, val) => acc.concat((val - mean) ** 2), []).reduce((acc, val) => acc + val, 0) / @@ -761,9 +761,9 @@ document.bodyShow examplesstandardDeviation([10, 2, 38, 23, 38, 23, 21]); // 13.284434142114991 (sample) standardDeviation([10, 2, 38, 23, 38, 23, 21], true); // 12.29899614287479 (population) -
Returns the sum of two or more numbers/arrays.
Use Array.reduce() to add each value to an accumulator, initialized with a value of 0.
const sum = (...arr) => [].concat(...arr).reduce((acc, val) => acc + val, 0); +
Returns the sum of two or more numbers/arrays.
Use Array.reduce() to add each value to an accumulator, initialized with a value of 0.
const sum = (...arr) => [].concat(...arr).reduce((acc, val) => acc + val, 0);
sum([1, 2, 3, 4]); // 10 -
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.
const sumPower = (end, power = 2, start = 1) => +
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.
const sumPower = (end, power = 2, start = 1) => Array(end + 1 - start) .fill(0) .map((x, i) => (i + start) ** power) @@ -771,20 +771,20 @@ document.bodyShow examplessumPower(10); // 385 sumPower(10, 3); //3025 sumPower(10, 3, 5); //2925 -
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.
const hasFlags = (...flags) => +
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.
const hasFlags = (...flags) => flags.every(flag => process.argv.includes(/^-{1,2}/.test(flag) ? flag : '--' + flag));
// node myScript.js -s --test --cool=true hasFlags('-s'); // true hasFlags('test', 'cool=true'); // true hasFlags('--test', 'cool=true', '-s'); // true hasFlags('special'); // false -
Writes a JSON object to a file.
Use fs.writeFile(), template literals and JSON.stringify() to write a json object to a .json file.
const fs = require('fs'); +
Writes a JSON object to a file.
Use fs.writeFile(), template literals and JSON.stringify() to write a json object to a .json file.
const fs = require('fs'); const JSONToFile = (obj, filename) => fs.writeFile(`${filename}.json`, JSON.stringify(obj, null, 2));
JSONToFile({ test: 'is passed' }, 'testJsonFile'); // writes the object to 'testJsonFile.json' -
Returns an array of lines from the specified file.
Use readFileSync function in fs node package to create a Buffer from a file. convert buffer to string using toString(encoding) function. creating an array from contents of file by spliting file content line by line (each \n).
const fs = require('fs'); +
Returns an array of lines from the specified file.
Use readFileSync function in fs node package to create a Buffer from a file. convert buffer to string using toString(encoding) function. creating an array from contents of file by spliting file content line by line (each \n).
const fs = require('fs'); const readFileLines = filename => fs .readFileSync(filename) @@ -799,15 +799,15 @@ contents of test.txt : */ let arr = readFileLines('test.txt'); console.log(arr); // ['line1', 'line2', 'line3'] -
Converts a tilde path to an absolute path.
Use String.replace() with a regular expression and OS.homedir() to replace the ~ in the start of the path with the home directory.
const untildify = str => str.replace(/^~($|\/|\\)/, `${require('os').homedir()}$1`); +
Converts a tilde path to an absolute path.
Use String.replace() with a regular expression and OS.homedir() to replace the ~ in the start of the path with the home directory.
const untildify = str => str.replace(/^~($|\/|\\)/, `${require('os').homedir()}$1`);
untildify('~/node'); // '/Users/aUser/node' -
Generates a UUID in Node.JS.
Use crypto API to generate a UUID, compliant with RFC4122 version 4.
const crypto = require('crypto'); +
Generates a UUID in Node.JS.
Use crypto API to generate a UUID, compliant with RFC4122 version 4.
const crypto = require('crypto'); const UUIDGeneratorNode = () => ([1e7] + -1e3 + -4e3 + -8e3 + -1e11).replace(/[018]/g, c => (c ^ (crypto.randomBytes(1)[0] & (15 >> (c / 4)))).toString(16) );
UUIDGeneratorNode(); // '79c7c136-60ee-40a2-beb2-856f1feabefc' -
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. Also if you give it a special key (childIndicator) it will search deeply inside it to apply function to inner objects too.
const cleanObj = (obj, keysToKeep = [], childIndicator) => { +
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. Also if you give it a special key (childIndicator) it will search deeply inside it to apply function to inner objects too.
const cleanObj = (obj, keysToKeep = [], childIndicator) => { Object.keys(obj).forEach(key => { if (key === childIndicator) { cleanObj(obj[key], keysToKeep, childIndicator); @@ -819,24 +819,24 @@ console.log< };
const testObj = { a: 1, b: 2, children: { a: 1, b: 2 } }; cleanObj(testObj, ['a'], 'children'); // { a: 1, children : { a: 1}} -
Inverts the key-value pairs of an object, without mutating it.
Use Object.keys() and Array.reduce() to invert the key-value pairs of an object.
const invertKeyValues = obj => +
Inverts the key-value pairs of an object, without mutating it.
Use Object.keys() and Array.reduce() to invert the key-value pairs of an object.
const invertKeyValues = obj => Object.keys(obj).reduce((acc, key) => { acc[obj[key]] = key; return acc; }, {});
invertKeyValues({ name: 'John', age: 20 }); // { 20: 'age', John: 'name' } -
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().
const lowercaseKeys = obj => +
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().
const lowercaseKeys = obj => Object.keys(obj).reduce((acc, key) => { acc[key.toLowerCase()] = obj[key]; return acc; }, {});
const myObj = { Name: 'Adam', sUrnAME: 'Smith' }; const myObjLower = lowercaseKeys(myObj); // {name: 'Adam', surname: 'Smith'}; -
Creates an object from the given key-value pairs.
Use Array.reduce() to create and combine key-value pairs.
const objectFromPairs = arr => arr.reduce((a, v) => ((a[v[0]] = v[1]), a), {}); +
Creates an object from the given key-value pairs.
Use Array.reduce() to create and combine key-value pairs.
const objectFromPairs = arr => arr.reduce((a, v) => ((a[v[0]] = v[1]), a), {});
objectFromPairs([['a', 1], ['b', 2]]); // {a: 1, b: 2} -
Creates an array of key-value pair arrays from an object.
Use Object.keys() and Array.map() to iterate over the object's keys and produce an array with key-value pairs.
const objectToPairs = obj => Object.keys(obj).map(k => [k, obj[k]]); +
Creates an array of key-value pair arrays from an object.
Use Object.keys() and Array.map() to iterate over the object's keys and produce an array with key-value pairs.
const objectToPairs = obj => Object.keys(obj).map(k => [k, obj[k]]);
objectToPairs({ a: 1, b: 2 }); // [['a',1],['b',2]]) -
Returns a sorted array of objects ordered by properties and orders.
Uses a custom implementation of sort, that reduces the props array argument with a default value of 0, it uses destructuring to swap the properties position depending on the order passed. If no orders array is passed it sort by 'asc' by default.
const orderBy = (arr, props, orders) => +
Returns a sorted array of objects ordered by properties and orders.
Uses a custom implementation of sort, that reduces the props array argument with a default value of 0, it uses destructuring to swap the properties position depending on the order passed. If no orders array is passed it sort by 'asc' by default.
const orderBy = (arr, props, orders) => [...arr].sort((a, b) => props.reduce((acc, prop, i) => { if (acc === 0) { @@ -854,15 +854,15 @@ console.log< ]; orderBy(users, ['name', 'age'], ['asc', 'desc']); // [{name: 'barney', age: 36}, {name: 'barney', age: 34}, {name: 'fred', age: 48}, {name: 'fred', age: 40}] orderBy(users, ['name', 'age']); // [{name: 'barney', age: 34}, {name: 'barney', age: 36}, {name: 'fred', age: 40}, {name: 'fred', age: 48}] -
Retrieve a property that indicated by the selector from an object.
If the property does not exists returns undefined.
const select = (from, selector) => +
Retrieve a property that indicated by the selector from an object.
If the property does not exists returns undefined.
const select = (from, selector) => selector.split('.').reduce((prev, cur) => prev && prev[cur], from);
const obj = { selector: { to: { val: 'val to select' } } }; select(obj, 'selector.to.val'); // 'val to select' -
Creates a shallow clone of an object.
Use Object.assign() and an empty object ({}) to create a shallow clone of the original.
const shallowClone = obj => Object.assign({}, obj); +
Creates a shallow clone of an object.
Use Object.assign() and an empty object ({}) to create a shallow clone of the original.
const shallowClone = obj => Object.assign({}, obj);
const a = { x: true, y: 1 }; const b = shallowClone(a); a === b; // false -
Get size of arrays, objects or strings.
Get type of value (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 value for strings.
Split strings into array of characters with split('') and return its length.
const size = value => +
Get size of arrays, objects or strings.
Get type of value (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 value for strings.
Split strings into array of characters with split('') and return its length.
const size = value => Array.isArray(value) ? value.length : value && typeof value === 'object' @@ -871,9 +871,9 @@ a === b;size([1, 2, 3, 4, 5]); // 5 size('size'); // 4 size({ one: 1, two: 2, three: 3 }); // 3 -
Checks if the predicate (second argument) is truthy on all elements of a collection (first argument).
Use Array.every() to check if each passed object has the specified property and if it returns a truthy value.
const truthCheckCollection = (collection, pre) => collection.every(obj => obj[pre]); +
Checks if the predicate (second argument) is truthy on all elements of a collection (first argument).
Use Array.every() to check if each passed object has the specified property and if it returns a truthy value.
const truthCheckCollection = (collection, pre) => collection.every(obj => obj[pre]);
truthCheckCollection([{ user: 'Tinky-Winky', sex: 'male' }, { user: 'Dipsy', sex: 'male' }], 'sex'); // true -
⚠️ 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 anagrams of a string (contains duplicates).
Use recursion. For each letter in the given string, create all the partial anagrams for the rest of its letters. Use Array.map() to combine the letter with each partial anagram, then Array.reduce() to combine all anagrams in one array. Base cases are for string length equal to 2 or 1.
const anagrams = str => { +
⚠️ 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 anagrams of a string (contains duplicates).
Use recursion. For each letter in the given string, create all the partial anagrams for the rest of its letters. Use Array.map() to combine the letter with each partial anagram, then Array.reduce() to combine all anagrams in one array. Base cases are for string length equal to 2 or 1.
const anagrams = str => { if (str.length <= 2) return str.length === 2 ? [str, str[1] + str[0]] : [str]; return str .split('') @@ -884,19 +884,19 @@ a === b;
anagrams('abc'); // ['abc','acb','bac','bca','cab','cba'] -
Returns the length of string.
Convert a given string to a Blob Object and find its size.
const byteSize = str => new Blob([str]).size; +
Returns the length of string.
Convert a given string to a Blob Object and find its size.
const byteSize = str => new Blob([str]).size;
byteSize('😀'); // 4 byteSize('Hello World'); // 11 -
Capitalizes the first letter of a string.
Use destructuring and 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.
const capitalize = ([first, ...rest], lowerRest = false) => +
Capitalizes the first letter of a string.
Use destructuring and 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.
const capitalize = ([first, ...rest], lowerRest = false) => first.toUpperCase() + (lowerRest ? rest.join('').toLowerCase() : rest.join(''));
capitalize('fooBar'); // 'FooBar' capitalize('fooBar', true); // 'Foobar' -
Capitalizes the first letter of every word in a string.
Use replace() to match the first character of each word and toUpperCase() to capitalize it.
const capitalizeEveryWord = str => str.replace(/\b[a-z]/g, char => char.toUpperCase()); +
Capitalizes the first letter of every word in a string.
Use replace() to match the first character of each word and toUpperCase() to capitalize it.
const capitalizeEveryWord = str => str.replace(/\b[a-z]/g, char => char.toUpperCase());
capitalizeEveryWord('hello world!'); // 'Hello World!' -
Retuns number of vowels in provided string.
Use a regular expression to count the number of vowels (A, E, I, O, U) in a string.
const countVowels = str => (str.match(/[aeiou]/gi) || []).length; +
Retuns number of vowels in provided string.
Use a regular expression to count the number of vowels (A, E, I, O, U) in a string.
const countVowels = str => (str.match(/[aeiou]/gi) || []).length;
countVowels('foobar'); // 3 countVowels('gym'); // 0 -
Escapes a string for use in HTML.
Use String.replace() with a regex 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).
const escapeHTML = str => +
Escapes a string for use in HTML.
Use String.replace() with a regex 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).
const escapeHTML = str => str.replace( /[&<>'"]/g, tag => @@ -909,9 +909,9 @@ a === b;}[tag] || tag) );
escapeHTML('<a href="#">Me & you</a>'); // '<a href="#">Me & you</a>' -
Escapes a string to use in a regular expression.
Use replace() to escape special characters.
const escapeRegExp = str => str.replace(/[.*+?^${}()|[\]\\]/g, '\\$&'); +
Escapes a string to use in a regular expression.
Use replace() to escape special characters.
const escapeRegExp = str => str.replace(/[.*+?^${}()|[\]\\]/g, '\\$&');
escapeRegExp('(test)'); // \\(test\\) -
Converts a string from camelcase.
Use replace() to remove underscores, hyphens, and spaces and convert words to camelcase. Omit the second argument to use a default separator of _.
const fromCamelCase = (str, separator = '_') => +
Converts a string from camelcase.
Use replace() to remove underscores, hyphens, and spaces and convert words to camelcase. Omit the second argument to use a default separator of _.
const fromCamelCase = (str, separator = '_') => str .replace(/([a-z\d])([A-Z])/g, '$1' + separator + '$2') .replace(/([A-Z]+)([A-Z][a-z\d]+)/g, '$1' + separator + '$2') @@ -919,17 +919,17 @@ a === b;fromCamelCase('someDatabaseFieldName', ' '); // 'some database field name' fromCamelCase('someLabelThatNeedsToBeCamelized', '-'); // 'some-label-that-needs-to-be-camelized' fromCamelCase('someJavascriptProperty', '_'); // 'some_javascript_property' -
Returns true if the given string is an absolute URL, false otherwise.
Use a regular expression to test if the string is an absolute URL.
const isAbsoluteURL = str => /^[a-z][a-z0-9+.-]*:/.test(str); +
Returns true if the given string is an absolute URL, false otherwise.
Use a regular expression to test if the string is an absolute URL.
const isAbsoluteURL = str => /^[a-z][a-z0-9+.-]*:/.test(str);
isAbsoluteURL('https://google.com'); // true isAbsoluteURL('ftp://www.myserver.net'); // true isAbsoluteURL('/foo/bar'); // false -
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 regex 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.
const mask = (cc, num = 4, mask = '*') => +
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 regex 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.
const mask = (cc, num = 4, mask = '*') => ('' + cc).slice(0, -num).replace(/./g, mask) + ('' + cc).slice(-num);
mask(1234567890); // '******7890' mask(1234567890, 3); // '*******890' mask(1234567890, 4, '$'); // '$$$$$$7890' mask(1234567890, -4, '$'); // '1234$$$$$$' -
Returns true if the given string is a palindrome, false otherwise.
Convert string toLowerCase() and use replace() to remove non-alphanumeric characters from it. Then, split('') into individual characters, reverse(), join('') and compare to the original, unreversed string, after converting it tolowerCase().
const palindrome = str => { +
Returns true if the given string is a palindrome, false otherwise.
Convert string toLowerCase() and use replace() to remove non-alphanumeric characters from it. Then, split('') into individual characters, reverse(), join('') and compare to the original, unreversed string, after converting it tolowerCase().
const palindrome = str => { const s = str.toLowerCase().replace(/[\W_]/g, ''); return ( s === @@ -940,7 +940,7 @@ a === b;
palindrome('taco cat'); // true -
If num is greater than 1 returns the plural form of the given string, else return the singular form.
Check if num is greater than 0. Throw an appropriate Error if not, return the appropriate string otherwise. Omit the third argument, items, to use a default plural form same as item suffixed with a single 's'.
const pluralize = (num, item, items = item + 's') => +
If num is greater than 1 returns the plural form of the given string, else return the singular form.
Check if num is greater than 0. Throw an appropriate Error if not, return the appropriate string otherwise. Omit the third argument, items, to use a default plural form same as item suffixed with a single 's'.
const pluralize = (num, item, items = item + 's') => num <= 0 ? (() => { throw new Error(`'num' should be >= 1. Value povided was ${num}.`); @@ -951,26 +951,26 @@ a === b;pluralize(2, 'apple'); // 'apples' pluralize(0, 'apple', 'apples'); // Gives error pluralize(-3, 'apple', 'apples'); // Gives error -
Repeats a string n times using String.repeat()
If no string is provided the default is "" and the default number of times is 2.
const repeatString = (str = '', num = 2) => { +
Repeats a string n times using String.repeat()
If no string is provided the default is "" and the default number of times is 2.
const repeatString = (str = '', num = 2) => { return num >= 0 ? str.repeat(num) : str; };
repeatString('abc', 3); // 'abcabcabc' repeatString('abc'); // 'abcabc' -
Reverses a string.
Use split('') and Array.reverse() to reverse the order of the characters in the string. Combine characters to get a string using join('').
const reverseString = str => +
Reverses a string.
Use split('') and Array.reverse() to reverse the order of the characters in the string. Combine characters to get a string using join('').
const reverseString = str => str .split('') .reverse() .join('');
reverseString('foobar'); // 'raboof' -
Alphabetically sorts the characters in a string.
Split the string using split(''), Array.sort() utilizing localeCompare(), recombine using join('').
const sortCharactersInString = str => +
Alphabetically sorts the characters in a string.
Split the string using split(''), Array.sort() utilizing localeCompare(), recombine using join('').
const sortCharactersInString = str => str .split('') .sort((a, b) => a.localeCompare(b)) .join('');
sortCharactersInString('cabbage'); // 'aabbceg' -
Splits a multiline string into an array of lines.
Use String.split() and a regular expression to match line breaks and create an array.
const splitLines = str => str.split(/\r?\n/); +
Splits a multiline string into an array of lines.
Use String.split() and a regular expression to match line breaks and create an array.
const splitLines = str => str.split(/\r?\n/);
splitLines('This\nis a\nmultiline\nstring.\n'); // ['This', 'is a', 'multiline', 'string' , ''] -
Converts a string to camelcase.
Break the string into words and combine them capitalizing the first letter of each word. For more detailed explanation of this Regex, visit this Site.
const toCamelCase = str => { +
Converts a string to camelcase.
Break the string into words and combine them capitalizing the first letter of each word. For more detailed explanation of this Regex, visit this Site.
const toCamelCase = str => { let s = str && str @@ -983,7 +983,7 @@ a === b;toCamelCase('Some label that needs to be camelized'); // 'someLabelThatNeedsToBeCamelized' toCamelCase('some-javascript-property'); // 'someJavascriptProperty' toCamelCase('some-mixed_string with spaces_underscores-and-hyphens'); // 'someMixedStringWithSpacesUnderscoresAndHyphens' -
Converts a string to kebab case.
Break the string into words and combine them using - as a separator. For more detailed explanation of this Regex, visit this Site.
const toKebabCase = str => +
Converts a string to kebab case.
Break the string into words and combine them using - as a separator. For more detailed explanation of this Regex, visit this Site.
const toKebabCase = str => str && str .match(/[A-Z]{2,}(?=[A-Z][a-z]+[0-9]*|\b)|[A-Z]?[a-z]+[0-9]*|[A-Z]|[0-9]+/g) @@ -994,7 +994,7 @@ a === b;toKebabCase('some-mixed_string With spaces_underscores-and-hyphens'); // 'some-mixed-string-with-spaces-underscores-and-hyphens' toKebabCase('AllThe-small Things'); // "all-the-small-things" toKebabCase('IAmListeningToFMWhileLoadingDifferentURLOnMyBrowserAndAlsoEditingSomeXMLAndHTML'); // "i-am-listening-to-fm-while-loading-different-url-on-my-browser-and-also-editing-xml-and-html" -
Converts a string to snake case.
Break the string into words and combine them using _ as a separator. For more detailed explanation of this Regex, visit this Site.
const toSnakeCase = str => +
Converts a string to snake case.
Break the string into words and combine them using _ as a separator. For more detailed explanation of this Regex, visit this Site.
const toSnakeCase = str => str && str .match(/[A-Z]{2,}(?=[A-Z][a-z]+[0-9]*|\b)|[A-Z]?[a-z]+[0-9]*|[A-Z]|[0-9]+/g) @@ -1006,10 +1006,10 @@ a === b;toSnakeCase('some-mixed_string With spaces_underscores-and-hyphens'); // 'some_mixed_string_with_spaces_underscores_and_hyphens' toSnakeCase('AllThe-small Things'); // "all_the_smal_things" toSnakeCase('IAmListeningToFMWhileLoadingDifferentURLOnMyBrowserAndAlsoEditingSomeXMLAndHTML'); // "i_am_listening_to_fm_while_loading_different_url_on_my_browser_and_also_editing_some_xml_and_html" -
Truncates a string up to a specified length.
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.
const truncateString = (str, num) => +
Truncates a string up to a specified length.
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.
const truncateString = (str, num) => str.length > num ? str.slice(0, num > 3 ? num - 3 : num) + '...' : str;
truncateString('boomerang', 7); // 'boom...' -
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).
const unescapeHTML = str => +
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).
const unescapeHTML = str => str.replace( /&|<|>|'|"/g, tag => @@ -1022,18 +1022,18 @@ a === b;}[tag] || tag) );
unescapeHTML('<a href="#">Me & you</a>'); // '<a href="#">Me & you</a>' -
Converts a given string into an array of words.
Use String.split() with a supplied pattern (defaults to non-alpha as a regex) to convert to an array of strings. Use Array.filter() to remove any empty strings. Omit the second argument to use the default regex.
const words = (str, pattern = /[^a-zA-Z-]+/) => str.split(pattern).filter(Boolean); +
Converts a given string into an array of words.
Use String.split() with a supplied pattern (defaults to non-alpha as a regex) to convert to an array of strings. Use Array.filter() to remove any empty strings. Omit the second argument to use the default regex.
const words = (str, pattern = /[^a-zA-Z-]+/) => str.split(pattern).filter(Boolean);
words('I love javaScript!!'); // ["I", "love", "javaScript"] words('python, javaScript & coffee'); // ["python", "javaScript", "coffee"] -
Clones a regular expression.
Use new RegExp(), RegExp.source and RegExp.flags to clone the given regular expression.
const cloneRegExp = regExp => new RegExp(regExp.source, regExp.flags); +
Clones a regular expression.
Use new RegExp(), RegExp.source and RegExp.flags to clone the given regular expression.
const cloneRegExp = regExp => new RegExp(regExp.source, regExp.flags);
const regExp = /lorem ipsum/gi; const regExp2 = cloneRegExp(regExp); // /lorem ipsum/gi -
Returns the first non-null/undefined argument.
Use Array.find() to return the first non null/undefined argument.
const coalesce = (...args) => args.find(_ => ![undefined, null].includes(_)); +
Returns the first non-null/undefined argument.
Use Array.find() to return the first non null/undefined argument.
const coalesce = (...args) => args.find(_ => ![undefined, null].includes(_));
coalesce(null, undefined, '', NaN, 'Waldo'); // "" -
Returns a customized coalesce function that returns the first argument that returns true from the provided argument validation function.
Use Array.find() to return the first argument that returns true from the provided argument validation function.
const coalesceFactory = valid => (...args) => args.find(valid); +
Returns a customized coalesce function that returns the first argument that returns true from the provided argument validation function.
Use Array.find() to return the first argument that returns true from the provided argument validation function.
const coalesceFactory = valid => (...args) => args.find(valid);
const customCoalesce = coalesceFactory(_ => ![null, undefined, '', NaN].includes(_)); customCoalesce(undefined, null, NaN, '', 'Waldo'); // "Waldo" -
Extends a 3-digit color code to a 6-digit color code.
Use Array.map(), split() and Array.join() to join the mapped array for converting a 3-digit RGB notated hexadecimal color-code to the 6-digit form. String.slice() is used to remove # from string start since it's added once.
const extendHex = shortHex => +
Extends a 3-digit color code to a 6-digit color code.
Use Array.map(), split() and Array.join() to join the mapped array for converting a 3-digit RGB notated hexadecimal color-code to the 6-digit form. String.slice() is used to remove # from string start since it's added once.
const extendHex = shortHex => '#' + shortHex .slice(shortHex.startsWith('#') ? 1 : 0) @@ -1042,15 +1042,15 @@ a === b;join('');
extendHex('#03f'); // '#0033ff' extendHex('05a'); // '#0055aa' -
Returns the native type of a value.
Returns lowercased constructor name of value, "undefined" or "null" if value is undefined or null
const getType = v => +
Returns the native type of a value.
Returns lowercased constructor name of value, "undefined" or "null" if value is undefined or null
const getType = v => v === undefined ? 'undefined' : v === null ? 'null' : v.constructor.name.toLowerCase();
getType(new Set([1, 2, 3])); // "set" -
Returns an object containing the parameters of the current URL.
Use 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.
const getURLParameters = url => +
Returns an object containing the parameters of the current URL.
Use 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.
const getURLParameters = url => url .match(/([^?=&]+)(=([^&]*))/g) .reduce((a, v) => ((a[v.slice(0, v.indexOf('='))] = v.slice(v.indexOf('=') + 1)), a), {});
getURLParameters('http://url.com/page?name=Adam&surname=Smith'); // {name: 'Adam', surname: 'Smith'} -
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.
const hexToRGB = hex => { +
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.
const hexToRGB = hex => { let alpha = false, h = hex.slice(hex.startsWith('#') ? 1 : 0); if (h.length === 3) h = [...h].map(x => x + x).join(''); @@ -1072,10 +1072,10 @@ a === b;hexToRGB('#27ae60ff'); // 'rgba(39, 174, 96, 255)' hexToRGB('27ae60'); // 'rgb(39, 174, 96)' hexToRGB('#fff'); // 'rgb(255, 255, 255)' -
Checks if the given argument is an array.
Use Array.isArray() to check if a value is classified as an array.
const isArray = val => !!val && Array.isArray(val); +
Checks if the given argument is an array.
Use Array.isArray() to check if a value is classified as an array.
const isArray = val => !!val && Array.isArray(val);
isArray(null); // false isArray([1]); // true -
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.
const isArrayLike = val => { +
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.
const isArrayLike = val => { try { return [...val], true; } catch (e) { @@ -1085,19 +1085,19 @@ a === b;isArrayLike(document.querySelectorAll('.className')); // true isArrayLike('abc'); // true isArrayLike(null); // false -
Checks if the given argument is a native boolean element.
Use typeof to check if a value is classified as a boolean primitive.
const isBoolean = val => typeof val === 'boolean'; +
Checks if the given argument is a native boolean element.
Use typeof to check if a value is classified as a boolean primitive.
const isBoolean = val => typeof val === 'boolean';
isBoolean(null); // false isBoolean(false); // true -
Checks if the given argument is a function.
Use typeof to check if a value is classified as a function primitive.
const isFunction = val => val && typeof val === 'function'; +
Checks if the given argument is a function.
Use typeof to check if a value is classified as a function primitive.
const isFunction = val => val && typeof val === 'function';
isFunction('x'); // false isFunction(x => x); // true -
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.
const isNull = val => val === null; +
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.
const isNull = val => val === null;
isNull(null); // true isNull('null'); // false -
Checks if the given argument is a number.
Use typeof to check if a value is classified as a number primitive.
const isNumber = val => typeof val === 'number'; +
Checks if the given argument is a number.
Use typeof to check if a value is classified as a number primitive.
const isNumber = val => typeof val === 'number';
isNumber('1'); // false isNumber(1); // true -
Returns a boolean determining if the supplied 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.
const isPrimitive = val => !['object', 'function'].includes(typeof val) || val === null; +
Returns a boolean determining if the supplied 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.
const isPrimitive = val => !['object', 'function'].includes(typeof val) || val === null;
isPrimitive(window.someNonExistentProperty); // true isPrimitive(null); // true isPrimitive(50); // true @@ -1106,7 +1106,7 @@ a === b;isPrimitive(Symbol()); // true isPrimitive([]); // false isPrimitive(new String('Hello!')); // false -
Returns true if an object looks like a Promise, false otherwise.
Check if the object is not null, its typeof matches either object or function and if it has a .then property, which is also a function.
const isPromiseLike = obj => +
Returns true if an object looks like a Promise, false otherwise.
Check if the object is not null, its typeof matches either object or function and if it has a .then property, which is also a function.
const isPromiseLike = obj => obj !== null && (typeof obj === 'object' || typeof obj === 'function') && typeof obj.then === 'function'; @@ -1117,13 +1117,13 @@ a === b; // true isPromiseLike(null); // false isPromiseLike({}); // false -
Checks if the given argument is a string.
Use typeof to check if a value is classified as a string primitive.
const isString = val => typeof val === 'string'; +
Checks if the given argument is a string.
Use typeof to check if a value is classified as a string primitive.
const isString = val => typeof val === 'string';
isString(10); // false isString('10'); // true -
Checks if the given argument is a symbol.
Use typeof to check if a value is classified as a symbol primitive.
const isSymbol = val => typeof val === 'symbol'; +
Checks if the given argument is a symbol.
Use typeof to check if a value is classified as a symbol primitive.
const isSymbol = val => typeof val === 'symbol';
isSymbol('x'); // false isSymbol(Symbol('x')); // true -
Checks if the provided argument is a valid JSON.
Use JSON.parse() and a try... catch block to check if the provided argument is a valid JSON.
const isValidJSON = obj => { +
Checks if the provided argument is a valid JSON.
Use JSON.parse() and a try... catch block to check if the provided argument is a valid JSON.
const isValidJSON = obj => { try { JSON.parse(obj); return true; @@ -1134,7 +1134,7 @@ a === b;isValidJSON('{"name":"Adam","age":20}'); // true isValidJSON('{"name":"Adam",age:"20"}'); // false isValidJSON(null); // true -
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.
const prettyBytes = (num, precision = 3, addSpace = true) => { +
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.
const prettyBytes = (num, precision = 3, addSpace = true) => { const UNITS = ['B', 'KB', 'MB', 'GB', 'TB', 'PB', 'EB', 'ZB', 'YB']; if (Math.abs(num) < 1) return num + (addSpace ? ' ' : '') + UNITS[0]; const exponent = Math.min(Math.floor(Math.log10(num < 0 ? -num : num) / 3), UNITS.length - 1); @@ -1147,16 +1147,16 @@ a === b;prettyBytes(27145424323.5821); // 27.1 GB prettyBytes(27145424323.5821, 5); // 27.145 GB prettyBytes(5500, 3, false); // 5.5KB -
Generates a random hexadecimal color code.
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).
const randomHexColorCode = () => { +
Generates a random hexadecimal color code.
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).
const randomHexColorCode = () => { let n = ((Math.random() * 0xfffff) | 0).toString(16); return '#' + (n.length !== 6 ? ((Math.random() * 0xf) | 0).toString(16) + n : n); };
randomHexColorCode(); // "#e34155" randomHexColorCode(); // "#fd73a6" randomHexColorCode(); // "#4144c6" -
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 padStart(6,'0') to get a 6-digit hexadecimal value.
const RGBToHex = (r, g, b) => ((r << 16) + (g << 8) + b).toString(16).padStart(6, '0'); +
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 padStart(6,'0') to get a 6-digit hexadecimal value.
const RGBToHex = (r, g, b) => ((r << 16) + (g << 8) + b).toString(16).padStart(6, '0');
RGBToHex(255, 165, 1); // 'ffa501' -
This algorithm is a simple hash-algorithm that hashes it input string s into a whole number.
Use split('') and Array.reduce() to create a hash of the input string, utilizing bit shifting.
const sdbm = str => { +
This algorithm is a simple hash-algorithm that hashes it input string s into a whole number.
Use split('') and Array.reduce() to create a hash of the input string, utilizing bit shifting.
const sdbm = str => { let arr = str.split(''); return arr.reduce( (hashCode, currentVal) => @@ -1166,7 +1166,7 @@ a === b;
console.log(sdbm('name')); // -3521204949 console.log(sdbm('age')); // 808122783 -
Measures the time taken by a function to execute.
Use console.time() and console.timeEnd() to measure the difference between the start and end times to determine how long the callback took to execute.
const timeTaken = callback => { +
Measures the time taken by a function to execute.
Use console.time() and console.timeEnd() to measure the difference between the start and end times to determine how long the callback took to execute.
const timeTaken = callback => { console.time('timeTaken'); const r = callback(); console.timeEnd('timeTaken'); @@ -1174,9 +1174,9 @@ console.log< };
timeTaken(() => Math.pow(2, 10)); // 1024 // (logged): timeTaken: 0.02099609375ms -
Use toLocaleString() to convert a float-point arithmetic to the Decimal mark form. It makes a comma separated string from a number.
const toDecimalMark = num => num.toLocaleString('en-US'); +
Use toLocaleString() to convert a float-point arithmetic to the Decimal mark form. It makes a comma separated string from a number.
const toDecimalMark = num => num.toLocaleString('en-US');
toDecimalMark(12305030388.9087); // "12,305,030,388.9087" -
Adds an ordinal suffix to a number.
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.
const toOrdinalSuffix = num => { +
Adds an ordinal suffix to a number.
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.
const toOrdinalSuffix = num => { const int = parseInt(num), digits = [int % 10, int % 100], ordinals = ['st', 'nd', 'rd', 'th'], @@ -1187,12 +1187,12 @@ console.log< : int + ordinals[3]; };
toOrdinalSuffix('123'); // "123rd" -
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.
const validateNumber = n => !isNaN(parseFloat(n)) && isFinite(n) && Number(n) == n; +
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.
const validateNumber = n => !isNaN(parseFloat(n)) && isFinite(n) && Number(n) == n;
validateNumber('10'); // true -
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.
const yesNo = (val, def = false) => +
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.
const yesNo = (val, def = false) => /^(y|yes)$/i.test(val) ? true : /^(n|no)$/i.test(val) ? false : def;
yesNo('Y'); // true yesNo('yes'); // true yesNo('No'); // false yesNo('Foo', true); // true -