JavaScript Array Methods Cheat Sheet

JS Array Methods Cheat Sheet

Every essential JavaScript array method with quick examples.

Transforming

map(fn)      // [1,2].map(x=>x*2) → [2,4]
filter(fn)   // [1,2,3].filter(x=>x>1) → [2,3]
reduce(fn,0) // [1,2,3].reduce((a,b)=>a+b) → 6
flat()       // [1,[2]].flat() → [1,2]

Finding

find(fn)      // first match
findIndex(fn) // index of first match
includes(x)   // true/false
indexOf(x)    // index or -1

Testing

some(fn)   // at least one matches
every(fn)  // all match

Adding/Removing

push(x)    // add to end
pop()      // remove from end
shift()    // remove from start
unshift(x) // add to start
splice(i,n)// remove/insert at index

Other

slice(a,b)  // copy portion (no mutate)
concat(arr) // merge arrays
join(",")   // array → string
reverse()   // reverse (mutates)
sort(fn)    // sort (mutates)

Mutating vs Non-Mutating

Mutates	Returns new
push, pop, splice, sort, reverse	map, filter, slice, concat

FAQs

map vs forEach?

map returns a new array; forEach returns nothing. More in our cheat sheets and JS guides.

Which methods mutate?

push, pop, shift, unshift, splice, sort, reverse.