# JS Quiz: Easy: Map key identity with NaN

**URL:** <https://forum.kirupa.com/t/js-quiz-easy-map-key-identity-with-nan/680502>\
**Category:** web dev\
**Created:** [April 16, 2026, 7:00am UTC](https://forum.kirupa.com/t/js-quiz-easy-map-key-identity-with-nan/680502 "2026-04-16T07:00:07Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![Yoshiii](https://yyz1.discourse-cdn.com/flex011/user_avatar/forum.kirupa.com/yoshiii/32/31156_2.png) [@Yoshiii](https://forum.kirupa.com/u/Yoshiii)\
**Post date:** [April 16, 2026, 7:00am UTC](https://forum.kirupa.com/t/js-quiz-easy-map-key-identity-with-nan/680502/1 "2026-04-16T07:00:07Z")

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What is printed?

```js
const m = new Map();
m.set(NaN, 'first');
m.set(NaN, 'second');
console.log(m.size, m.get(NaN));

```

_Poll ([view on site](https://forum.kirupa.com/t/js-quiz-easy-map-key-identity-with-nan/680502/1))_

Yoshiii

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<div class="post-metadata">

**Author:** ![BobaMilk](https://yyz1.discourse-cdn.com/flex011/user_avatar/forum.kirupa.com/bobamilk/32/31157_2.png) [@BobaMilk](https://forum.kirupa.com/u/BobaMilk)\
**Post date:** [April 16, 2026, 7:35am UTC](https://forum.kirupa.com/t/js-quiz-easy-map-key-identity-with-nan/680502/2 "2026-04-16T07:35:18Z")

</div>

It prints `1 second` since `Map` treats `NaN` as the same key and the second `set` overwrites the first.

@Yoshiii the `size` stays 1 and `get(NaN)` returns `second`.

BobaMilk