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JavaScript Array Methods Cheat Sheet

Array methods grouped by what they do, with a note on whether each one changes the original array.

Put it into practice with the matching tool.

Adding & removing

push(x)Add to the end — mutates

pop()Remove the last item — mutates

unshift(x)Add to the start — mutates

shift()Remove the first item — mutates

splice(i, n, ...items)Remove/insert at an index — mutates

slice(start, end)Copy a portion — does not mutate

concat(arr)Join arrays into a new one

map(fn)New array with each item transformed

filter(fn)New array with only items that pass the test

reduce(fn, init)Collapse the array into a single value

flat(depth)Flatten nested arrays

flatMap(fn)Map then flatten one level

join(sep)Combine into a string

find(fn)First item matching the test (or undefined)

findIndex(fn)Index of the first match (or -1)

findLast(fn)Last item matching the test

indexOf(x)Index of a value (or -1)

includes(x)True if the value exists

forEach(fn)Run a function for each item (returns undefined)

some(fn)True if at least one item passes

every(fn)True if all items pass

Array.isArray(x)Check whether a value is an array

sort((a,b) => a - b)Sort numerically — mutates

sort()Sorts as strings by default (10 before 2)

reverse()Reverse in place — mutates

toSorted() / toReversed()Newer non-mutating versions

Array.from(x)Build an array from an iterable or array-like

Array.from({length: 5}, (_, i) => i)Generate [0,1,2,3,4]

Array.of(1, 2)Create an array from arguments

[...new Set(arr)]Remove duplicates