JavaScript Array Methods Cheat Sheet

const arr = [1, 3, 5, 7];
const arr2 = [1, 3, 5, 5, 7];
const arr3 = ['d', 'a', 'b', 'c'];
const arr4 = [1, 30, 2, 100];
const users = [
	{ name: 'grace', city: 'Toronto', age: 30 },
	{ name: 'monica', city: 'New York', age: 24 },
];

Method	Code Example	Result	Return Type	In Place
keys()	const iterator = arr.keys(); for (const key of iterator) { console.log(key); }	0 1 2 3	Array Iterator	No
values()	const iterator = arr.values(); for (const value of iterator) { console.log(value); }	1 3 5 7	Array Iterator	No
push()	console.log(arr.push(9)); console.log(arr);	5 // new length of the array [1, 3, 5, 7, 9]	number	No
pop()	console.log(arr.pop()); console.log(arr);	7 // last element of the array [1, 3, 5]	element	No
shift()	console.log(arr.shift()); console.log(arr);	1 // removed element [3, 5, 7]	element	No
unshift()	console.log(arr.unshift(2, 4)); console.log(arr);	6 // new length of the array [2, 4, 1, 3, 5, 7]	number	No
slice()	console.log(arr.slice(1, 3)); console.log(arr); // remain from index 1 to 2 (last one is not included)	[3, 5] [ 1, 3, 5, 7 ]	array	No
splice()	arr.splice(1, 0, 2); // insert ‘2’ at index 1 console.log(arr);	[1, 2, 3, 5, 7]	array	Yes
splice()	arr.splice(3, 1, 4); // replace 1 item at index 3 console.log(arr);	[1, 3, 5, 4]	array	Yes
splice()	console.log(arr.splice(1, 2)); // remove 2 items from index 1 console.log(arr);	[3, 5] // removed items [1, 7] // array as a result	array	Yes
join()	console.log(arr.join());	1,3,5,7	string	No
indexOf()	console.log(arr.indexOf(3));	1	number	No
lastIndexOf()	console.log(arr2.lastIndexOf(5));	3	number	No
reduce()	console.log(arr.reduce((pre, curr) => pre + curr));	16	number	No
find()	console.log(arr.find((num) => num > 3));	5	first one	No
findIndex()	console.log(arr.findIndex((num) => num > 3));	2	first one	No
every()	console.log(arr.every((num) => num % 2 === 1));	TRUE	boolean	No
every()	console.log(arr.every((num) => num > 10));	FALSE	boolean	No
some()	console.log(arr.some((num) => num > 5));	TRUE	boolean	No
filter()	console.log(arr.filter((num) => num > 3)); const newUsers = users.filter((user) => user.age > 25); console.log(newUsers);	[5, 7] [ { name: 'grace', city: 'Toronto', age: 30 } ]	array	No
map()	arr.map((item) => item * 2) users.map((user) => console.log(user.name));	[2, 6, 10, 14] grace monica	array	No
flatMap()	console.log(arr.flatMap((x) => [x, x * 2]));	[1, 2, 3, 6, 5, 10, 7, 14]	array	No
forEach()	arr.forEach((item) => console.log(item * 2));	2 6 10 14	each element	No
includes()	console.log(arr.includes(3));	TRUE	boolean	No
isArray()	console.log(Array.isArray([1, 2, 3]));	TRUE	boolean	No
reverse()	console.log(arr.reverse());	[7, 5, 3, 1]	array	Yes
concat()	const newArr = arr.concat(['a', 'b']); console.log(newArr);	[1, 3, 5, 7, "a", "b"]	array	No
fill()	console.log(arr.fill('a', 1, 3)); // fill with 'a' from position 1 until position 3	[1, "a", "a", 7]	array	No
flat()	const newArr = [1, 3, 5, 7, [2, 4]]; console.log(newArr.flat());	[1, 3, 5, 7, 2, 4]	array	No
Array.from()	console.log(Array.from([1, 2, 3], (x) => x * 2));	[2, 4, 6]	array	No
Array.from()	console.log(Array.from('grace'));	["g", "r", "a", "c", "e"]	array	No
sort()	console.log(arr3.sort());	["a", "b", "c", "d"]	array	Yes
sort()	console.log(arr4.sort()); console.log(arr4.sort((a, b) => a - b));	[ 1, 100, 2, 30 ] [1, 2, 30, 100]	array	Yes