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)))
+// 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.
Removes elements in an array until the passed function returns true. Returns the remaining elements in the array.
Loop through the array, using Array.shift() to drop the first element of the array until the returned value from the function is true.
+
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.shift();
+ 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
Check if n is shorter than the given array and use Array.slice() to slice it accordingly or return an empty array.
const dropRight = (arr, n = 1) => n < arr.length ? arr.slice(0, arr.length - 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.
Array.reduce() to create an object, where the keys are produced
// initial([1,2,3]) -> [1,2]
Initializes an array containing the numbers in the specified range.
-Use Array(end-start) to create an array of the desired length, Array.map() to fill with the desired values in a range.
+
Initializes an array containing the numbers in the specified range where start and end are inclusive.
Use Array((end + 1) - start) to create an array of the desired length, Array.map() to fill with the desired values in a range.
You can omit start to use a default value of 0.
const initializeArrayWithRange = (end, start = 0) =>
- Array.from({ length: end - start }).map((v, i) => i + start);
-// initializeArrayWithRange(5) -> [0,1,2,3,4]
+const initializeArrayWithRange = (end, start = 0) =>
+ Array.from({ length: (end + 1) - start }).map((v, i) => i + start);
+// initializeArrayWithRange(5) -> [0,1,2,3,4,5]
+// initializeArrayWithRange(7, 3) -> [3,4,5,6,7]
Initializes and fills an array with the specified values.
@@ -334,6 +354,7 @@ Omit the second argument,n, to get the first element of the array.
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 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 pulled = arr.filter((v, i) => !args.includes(v));
arr.length = 0; pulled.forEach(v => arr.push(v));
@@ -342,6 +363,38 @@ Use Array.length = 0 to mutate the passed in array by resetting it'
// pull(myArray, 'a', 'c');
// console.log(myArray) -> [ 'b', 'b' ]
Mutates the original array to filter out the values specified (accepts an array of values).
+Use Array.filter() and Array.includes() to pull out the values that are not needed.
+Use Array.length = 0 to mutate the passed in array by resetting it's length to zero and Array.push() to re-populate it with only the pulled values.
const pullAll = (arr, pullArr) => {
+ let pulled = arr.filter((v, i) => !pullArr.includes(v));
+ arr.length = 0; pulled.forEach(v => arr.push(v));
+}
+// let myArray = ['a', 'b', 'c', 'a', 'b', 'c'];
+// pullAll(myArray, ['a', 'c']);
+// console.log(myArray) -> [ '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 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)
+ .filter((v, i) => !pullArr.includes(i))
+ arr.length = 0;
+ pulled.forEach(v => arr.push(v));
+ return removed;
+}
+
+// let myArray = ['a', 'b', 'c', 'd'];
+// let pulled = pullAtIndex(myArray, [1, 3]);
+
+// console.log(myArray); -> [ 'a', 'c' ]
+// console.log(pulled); -> [ 'b', 'd' ]
+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().
@@ -411,6 +464,7 @@ This method also works with strings.
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]
undefined is used where no
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;
+ document.documentElement.clientHeight + window.scrollY >= (document.documentElement.scrollHeight || document.documentElement.clientHeight);
// bottomVisible() -> true
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);
+ 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
@@ -842,6 +896,15 @@ Also if you give it a special key (childIndicator) it will search d
const objectToPairs = obj => Object.keys(obj).map(k => [k, obj[k]]);
// objectToPairs({a: 1, b: 2}) -> [['a',1],['b',2]])
+Retrieve a property that indicated by the selector from object.
+If property 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.
lowerRest parameter to keep the rest of the string intact,
Retuns number of vowels in provided string.
Use a regular expression to count number of vowels (A, E, I, O, U) in a string.
const countVowels = str =>
- return (str.match(/[aeiou]/ig) || []).length;
+const countVowels = str => (str.match(/[aeiou]/ig) || []).length;
// countVowels('foobar') -> 3
// countVowels('gym') -> 0
@@ -914,9 +976,9 @@ Omit the second argument to use a default separator of _.
Reverses a string.
-Use array destructuring and Array.reverse() to reverse the order of the characters in the 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].reverse().join('');
+const reverseString = str => str.split('').reverse().join('');
// reverseString('foobar') -> 'raboof'