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A One-Minute Primer on the JavaScript Array Map, Filter, and Reduce Methods

nas5w profile image Nick Scialli (he/him) ・1 min read

Map, Filter, and Reduce are powerful array methods that are definitely worth learning! This is a super-quick primer on each method.

map: return array where each element is transformed as specified by the function

const arr = [1, 2, 3, 4, 5, 6];
const mapped = arr.map(el => el + 20);
console.log(mapped);
// [21, 22, 23, 24, 25, 26]

filter: return array of elements where the function returns true

const arr = [1, 2, 3, 4, 5, 6];
const filtered = arr.filter(el => el === 2 || el === 4);
console.log(filtered);
// [2, 4]

reduce: accumulate values as specified in function

const arr = [1, 2, 3, 4, 5, 6];
const reduced = arr.reduce((total, current) => total + current, 0);
console.log(reduced);
// 21

More arguments

Note that this is the most basic use of the map, filter, and reduce methods and the functions passed to them can take additional arguments. In other words, please treat this post as a basic introduction!

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