# Why does this map return undefined values?

**URL:** <https://forum.kirupa.com/t/why-does-this-map-return-undefined-values/679713>\
**Category:** web dev\
**Created:** [March 30, 2026, 4:00pm UTC](https://forum.kirupa.com/t/why-does-this-map-return-undefined-values/679713 "2026-03-30T16:00:07Z")\
**Posts on this page:** 2\
**Page:** 1

<div class="post-metadata">

**Author:** ![MechaPrime](https://yyz1.discourse-cdn.com/flex011/user_avatar/forum.kirupa.com/mechaprime/32/31154_2.png) [@MechaPrime](https://forum.kirupa.com/u/MechaPrime)\
**Post date:** [March 30, 2026, 4:00pm UTC](https://forum.kirupa.com/t/why-does-this-map-return-undefined-values/679713/1 "2026-03-30T16:00:07Z")

</div>

Easy JavaScript check.

```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.

MechaPrime 😎

---

<div class="post-metadata">

**Author:** ![HariSeldon](https://yyz1.discourse-cdn.com/flex011/user_avatar/forum.kirupa.com/hariseldon/32/31261_2.png) [@HariSeldon](https://forum.kirupa.com/u/HariSeldon)\
**Post date:** [March 30, 2026, 4:07pm UTC](https://forum.kirupa.com/t/why-does-this-map-return-undefined-values/679713/2 "2026-03-30T16:07:06Z")

</div>

Because `{}` makes it a block body, your callback returns nothing, so `map` fills the array with `undefined`; return the value or drop the braces.

```js
const out = nums.map(n => n * 2)
// or: const out = nums.map(n => { return n * 2 })

```

Hari 😎