All Cheat Sheets
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 elementflatMap()
arr.flatMap(x => [x, x*2])Map then flatten one levelflat()
arr.flat(Infinity)Flatten nested arraysFilter & Find
filter()
arr.filter(x => x > 5)Keep elements passing testfind()
arr.find(x => x.id === 1)First element passing testfindIndex()
arr.findIndex(x => x > 3)Index of first matchincludes()
arr.includes(3)Check if value existssome()
arr.some(x => x > 10)Any element passes test?every()
arr.every(x => x > 0)All elements pass test?Reduce
reduce()
arr.reduce((sum, x) => sum + x, 0)Reduce to single valuereduceRight()
arr.reduceRight((a, x) => a + x, '')Reduce right-to-leftAdd & Remove
push()
arr.push(4)Add to end, returns lengthpop()
arr.pop()Remove from end, returns elementunshift()
arr.unshift(0)Add to startshift()
arr.shift()Remove from startsplice()
arr.splice(1, 2, 'a')Add/remove at indexconcat()
arr.concat([4, 5])Merge arraysSort & Order
sort()
arr.sort((a,b) => a - b)Sort in placereverse()
arr.reverse()Reverse in placetoSorted()
arr.toSorted((a,b) => a-b)Sort (immutable, ES2023)toReversed()
arr.toReversed()Reverse (immutable, ES2023)Iterate
forEach()
arr.forEach(x => console.log(x))Execute for each elemententries()
[...arr.entries()]Iterator of [index, value]keys()
[...arr.keys()]Iterator of indicesvalues()
[...arr.values()]Iterator of valuesCreate & Convert
Array.from()
Array.from({length:5}, (_,i) => i)Create from iterableArray.of()
Array.of(1, 2, 3)Create from argumentsslice()
arr.slice(1, 3)Shallow copy portionjoin()
arr.join(', ')Join as stringat()
arr.at(-1)Element at index (supports negative)