JavaScript Array Methods

Quick reference for JS array methods — map, filter, reduce, find, sort, flat, and more.

Transform

map()arr.map(x => x * 2)Create new array by transforming each element

flatMap()arr.flatMap(x => [x, x*2])Map then flatten one level

flat()arr.flat(Infinity)Flatten nested arrays

filter()arr.filter(x => x > 5)Keep elements passing test

find()arr.find(x => x.id === 1)First element passing test

findIndex()arr.findIndex(x => x > 3)Index of first match

includes()arr.includes(3)Check if value exists

some()arr.some(x => x > 10)Any element passes test?

every()arr.every(x => x > 0)All elements pass test?

reduce()arr.reduce((sum, x) => sum + x, 0)Reduce to single value

reduceRight()arr.reduceRight((a, x) => a + x, '')Reduce right-to-left

push()arr.push(4)Add to end, returns length

pop()arr.pop()Remove from end, returns element

unshift()arr.unshift(0)Add to start

shift()arr.shift()Remove from start

splice()arr.splice(1, 2, 'a')Add/remove at index

concat()arr.concat([4, 5])Merge arrays

sort()arr.sort((a,b) => a - b)Sort in place

reverse()arr.reverse()Reverse in place

toSorted()arr.toSorted((a,b) => a-b)Sort (immutable, ES2023)

toReversed()arr.toReversed()Reverse (immutable, ES2023)

forEach()arr.forEach(x => console.log(x))Execute for each element

entries()[...arr.entries()]Iterator of [index, value]

keys()[...arr.keys()]Iterator of indices

values()[...arr.values()]Iterator of values

Array.from()Array.from({length:5}, (_,i) => i)Create from iterable

Array.of()Array.of(1, 2, 3)Create from arguments

slice()arr.slice(1, 3)Shallow copy portion

join()arr.join(', ')Join as string

at()arr.at(-1)Element at index (supports negative)

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