# JS Tip of the Day: What is a NaN?

**URL:** https://forum.kirupa.com/t/js-tip-of-the-day-what-is-a-nan/643099
**Category:** web dev
**Created:** [May 7, 2020, 3:35pm UTC](https://forum.kirupa.com/t/js-tip-of-the-day-what-is-a-nan/643099 "2020-05-07T15:35:21Z")
**Posts on this page:** 1
**Page:** 1

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### Author: ![senocular](https://yyz1.discourse-cdn.com/flex011/user_avatar/forum.kirupa.com/senocular/32/7217_2.png) [@senocular](https://forum.kirupa.com/u/senocular)
#### Post date: [May 7, 2020, 3:35pm UTC](https://forum.kirupa.com/t/js-tip-of-the-day-what-is-a-nan/643099/1 "2020-05-07T15:35:21Z")

</div>

**What is a NaN?**  
Level: Beginner

In JavaScript `NaN` stands for _Not a Number_. Its a primitive value that is used to represent a non-number value within the number type. So in reality, `NaN` is both a number, and not.

The value `NaN` is accessible both as a global and as a property of `Number`.

```javascript
console.log(NaN); // NaN
console.log(Number.NaN); // NaN
console.log(typeof NaN); // number

```

Any time you perform a numeric operation that can’t resolve into a number, you’ll get `NaN` as a result.

```javascript
console.log(1 * 'x'); // NaN
console.log(0/0); // NaN
console.log(Math.sqrt(-1)); // NaN

```

If you try to convert a value that can’t be turned into a number, you’ll also get a `NaN` value in return.

```javascript
console.log(Number('x')); // NaN
console.log(+{}); // NaN

```

The value `NaN` has a peculiar behavior where its not equal to itself.

```javascript
console.log(NaN === NaN); // false

```

To see if something is `NaN`, instead of comparing it to `NaN`, you can use an `isNaN()` function. There are also two of these, one global and one in `Number`, though they work slightly differently. The global `isNaN()` will first try to convert a value to a number and then see if the result is `NaN` whereas `Number.isNaN()` will check specifically to see if the value its given is the value `NaN`.

```javascript
console.log(isNaN(NaN)); // true
console.log(isNaN('1')); // false
console.log(isNaN('x')); // true

console.log(Number.isNaN(NaN)); // true
console.log(Number.isNaN('1')); // false
console.log(Number.isNaN('x')); // false

```

More info:

- [NaN on MDN](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/NaN)
- [Number.NaN on MDN](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number/NaN)
- [isNaN() on MDN](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/isNaN)
- [Number.isNaN() on MDN](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number/isNaN)