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JavaScript Array Functions Cheat Sheet

concat()
> 96%

merge two or more arrays
[ 1, 2 ].concat([5], [7, 9]) // [ 1, 2, 5, 7, 9 ]
const new_array = old_array.concat([value1[, value2[, ...[, valueN]]]])

copyWithin()
> 92%

copies part of array to another location
[ 1, 2, 3, 4, 5 ].copyWithin(0,2)  // [ 3, 4, 5, 4, 5 ]
arr.copyWithin(target[, start[, end]])
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entries()
> 94%

Array Iterator with key/value pairs for each index
['a', 'b', 'c']
	.entries() // Array Iterator {  }
	.next() // { value: (2) […], done: false }
	.value // Array [ 0, "a" ]
arr.entries()

every()
> 95%

tests if all elements in the array pass the test
[1, 30, 40].every(val => val > 0) // true
arr.every(callback(element[, index[, array]])[, thisArg])

fill()
> 92%

changes elements in an array to a static value
[1, 2, 3, 4].fill('x', 1, 3) // [ 1, "x", "x", 4 ]
arr.fill(value[, start[, end]])

filter()
> 95%

creates new array with elements that pass test
[1, 10, 5, 6].filter(val => val > 5) // [ 10, 6 ]
let newArray = arr.filter(callback(element[, index, [array]])[, thisArg])

find()
> 95%

returns the value of the first element, that matches test
[1, 10, 5, 6].find(val => val > 5) // 10
arr.find(callback(element[, index[, array]])[, thisArg])

findIndex()
> 94%

returns index of the first element, that matches test
[1, 4, 5, 6].findIndex(val => val > 5) // 3
arr.findIndex(callback( element[, index[, array]] )[, thisArg])

flat()
> 87%

creates a new array with sub-array elements flattened by specified depth.
[1, [2, [3, [4]]]].flat(2) // [ 1, 2, 3, [4] ]
const new_array = arr.flat([depth]);

flatMap()
> 87%

creates a new array with sub-array elements flattened by specified depth.
[[2], [4], [6], [8]].flatMap(val => val/2) // [ 1, 2, 3, 4 ]
var new_array = arr.flatMap(function callback(currentValue[, index[, array]]) {
    // return element for new_array
}[, thisArg])

forEach()
> 95%

executes provided function once for each array element
[ 1, 2, 3 ].forEach(val => console.log(val)) // 1 // 2 // 3
arr.forEach(callback(currentValue [, index [, array]])[, thisArg])

includes()
> 95%

determines if array includes a certain value
[ 1, 2, 3 ].includes(3) // true
arr.includes(valueToFind[, fromIndex])

indexOf()
> 95%

returns the first index at which element can be found
[ 1, 2, 3 ].indexOf(3) // 2
arr.indexOf(searchElement[, fromIndex])

join()
> 96%

returns string by concatenating all elements in array
[ "x", "y", "z" ].join(" - ") // "x - y - z"
arr.join([separator])

keys()
> 93%

returns Array Iterator that contains keys for each index
['a', 'b', 'c']
	.keys() // Array Iterator {  }
	.next() // { value: 0, done: false }
	.value // 0
arr.keys()

lastIndexOf()
> 95%

returns last index at which given element can be found
[ 1, 2, 3, 1, 0].lastIndexOf(1) // 3
arr.lastIndexOf(searchElement[, fromIndex])

map()
> 95%

creates new array with results of provided function
[ 2, 3, 4 ].map(val => val * 2) // [ 4, 6, 8 ]
let new_array = arr.map(function callback( currentValue[, index[, array]]) {
    // return element for new_array
}[, thisArg])

pop()
> 96%

removes last element from array and returns that element
const arr = [ 1, 2, 3 ]
arr.pop() // returns: 3 // arr is [ 1, 2 ]
arr.pop()

push()
> 96%

adds one or more elements to end of array and returns new length
const arr = [ 1, 2, 3 ]
arr.push(1) // returns: 4 // arr is [ 1, 2, 3, 4 ]
arr.push(element1[, ...[, elementN]])

reduce()
> 95%

executes a reducer function, resulting in single output value
[ 'a', 'b', 'c' ].reduce((acc, curr) => acc + curr, 'd') // "dabc"
arr.reduce(callback( accumulator, currentValue[, index[, array]] )[, initialValue])

reduceRight()
> 95%

executes a reducer function from right to left, resulting in single output value
[ 'a', 'b', 'c' ].reduceRight((acc, curr) => acc + curr, 'd') // "dcba"
arr.reduceRight(callback(accumulator, currentValue[, index[, array]])[, initialValue])

reverse()
> 96%

reverses an array
[ 1, 2, 3 ].reverse() // [ 3, 2, 1 ]
arr.reverse()

shift()
> 96%

removes the first element from array and returns that element
const arr = [ 1, 2, 3 ]
arr.shift() // returns: 1 // arr is [ 2, 3 ]
arr.shift()

slice()
> 96%

returns a copy of part of array, while original array is not modified
[ 1, 2, 3, 4 ].slice(1, 3) // [ 2, 3 ]
arr.slice([begin[, end]])

some()
> 95%

tests whether at least one element in array passes the test
[ 1, 2, 3, 4 ].some(val => val > 3) // true
arr.some(callback(element[, index[, array]])[, thisArg])

sort()
> 96%

sorts the elements of array in place
[ 1, 2, 3, 4 ].sort((a, b) => b - a) // [ 4, 3, 2, 1 ]
arr.sort([compareFunction])

splice()
> 96%

changes contents of array by removing, replacing and/or adding elements
const arr = [ 1, 2, 3, 4 ]
arr.splice(1, 2, 'a') // returns [ 2, 3 ] // arr is [ 1, "a", 4 ]
let arrDeletedItems = array.splice(start[, deleteCount[, item1[, item2[, ...]]]])

toLocaleString()
> 95%

elements are converted to Strings using toLocaleString and are separated by locale-specific String (eg. “,”)
[1.1, 'a', new Date()].toLocaleString('EN') // "1.1,a,5/18/2020, 7:58:57 AM"
arr.toLocaleString([locales[, options]]);

toString()
> 95%

returns a string representing the specified array
[ 'a', 2, 3 ].toString() // "a,2,3"
arr.toString()

unshift()
> 96%

adds one or more elements to beginning of array and returns new length
const arr = [ 1, 2, 3 ]
arr.unshift(0, 99) // returns 5 // arr is [ 0, 99, 1, 2, 3 ]
arr.unshift(element1[, ...[, elementN]])

values()
> 91%

returns Array Iterator object that contains values for each index in array
['a', 'b', 'c']
	.values() // Array Iterator {  }
	.next() // { value: "a", done: false }
	.value // "a"
arr.values()