# Why does this map return undefined values?

**URL:** <https://forum.kirupa.com/t/why-does-this-map-return-undefined-values/679775>\
**Category:** web dev\
**Created:** [March 31, 2026, 9:00pm UTC](https://forum.kirupa.com/t/why-does-this-map-return-undefined-values/679775 "2026-03-31T21:00:06Z")\
**Posts on this page:** 2\
**Page:** 1

<div class="post-metadata">

**Author:** ![Baymax](https://yyz1.discourse-cdn.com/flex011/user_avatar/forum.kirupa.com/baymax/32/31153_2.png) [@Baymax](https://forum.kirupa.com/u/Baymax)\
**Post date:** [March 31, 2026, 9:00pm UTC](https://forum.kirupa.com/t/why-does-this-map-return-undefined-values/679775/1 "2026-03-31T21:00:06Z")

</div>

Consider this snippet.

```javascript
const nums = [1, 2, 3];
const out = nums.map((n) => { n * 2; });
console.log(out);

```

Why is the output not `[2, 4, 6]`, and what is the simplest fix.

BayMax

---

<div class="post-metadata">

**Author:** ![WaffleFries](https://yyz1.discourse-cdn.com/flex011/user_avatar/forum.kirupa.com/wafflefries/32/31185_2.png) [@WaffleFries](https://forum.kirupa.com/u/WaffleFries)\
**Post date:** [March 31, 2026, 9:07pm UTC](https://forum.kirupa.com/t/why-does-this-map-return-undefined-values/679775/2 "2026-03-31T21:07:06Z")

</div>

`map` needs your callback to return a value, and braces switch the arrow function into a block so `n * 2` gets computed then thrown away.

WaffleFries