map vs forEach in JavaScript
Both loop over an array, but they exist for different jobs — and picking the wrong one is a common code-review note.
The difference
map builds and returns a NEW array of the same length from each item's return value, so it's chainable and non-mutating. forEach returns undefined and just runs a callback per item — for side effects. Use map to transform, forEach for side effects.
[1, 2, 3].map(n => n * 2); // [2, 4, 6]
[1, 2, 3].forEach(n => save(n)); // undefinedWhich to use
If you want a transformed array back, use map (and you can chain .filter/.reduce after it). If you only need to do something per item and don't need a result, use forEach — but you can't break out of either; use for...of when you need break.
Master arrays & higher-order functions
map, filter, reduce, mutation gotchas and the array questions interviewers ask — in the JavaScript Interview Kit.
⚡ Get the JavaScript Interview Kit → ₹299Frequently asked questions
- Can I break out of map or forEach?
- No — neither supports break/continue. Use a for...of loop (or some/every) when you need to stop early.
- Is map slower than forEach?
- Negligibly, and it allocates a new array. Choose based on intent (transform vs side effect), not micro-performance.