JavaScript Array Methods Cheat Sheet

[Lomanu4]

Method	Purpose	Example Usage	Returns
map()	Transforms each element and returns a new array	arr.map(x => x * 2)	New array
filter()	Returns array of elements that pass the test in the callback	arr.filter(x => x > 0)	New array
reduce()	Reduces array to single value by applying a function	arr.reduce((a, b) => a + b, 0)	Single value
forEach()	Runs a function on each array element (no return)	arr.forEach(x => console.log(x))	undefined
find()	Finds the first element that passes the test	arr.find(x => x > 10)	Element or undefined
findIndex()	Finds the index of the first element passing the test	arr.findIndex(x => x > 10)	Index or -1
some()	Checks if any element passes the test	arr.some(x => x < 0)	true/false
every()	Checks if all elements pass the test	arr.every(x => x > 0)	true/false
includes()	Checks if array contains a value	arr.includes(2)	true/false
indexOf()	Finds index of value in array (-1 if not found)	arr.indexOf(2)	Index or -1
push()	Adds elements to end, returns new length	arr.push(4)	New length
pop()	Removes last element, returns removed value	arr.pop()	Removed element
shift()	Removes first element, returns removed value	arr.shift()	Removed element
unshift()	Adds elements to start, returns new length	arr.unshift(1)	New length
slice()	Returns part of array, does not modify original	arr.slice(1, 3)	New array
splice()	Changes array by adding/removing elements	arr.splice(1, 2)	Removed elements
concat()	Combines arrays, returns new array	arr.concat([4,5])	New array
join()	Joins all elements into a string	arr.join('-')	String
reverse()	Reverses array in place	arr.reverse()	Same array
sort()	Sorts array in place	arr.sort()	Same array
flat()	Flattens nested arrays	arr.flat()	New array
fill()	Fills array with static value	arr.fill(0)	Same array
from()	Creates array from array-like object	Array.from('abc')	New array
isArray()	Checks if a value is an array	Array.isArray(arr)	true/false

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