content/snippets/js/s/value-not-equal-to-itself.md
---
title: What is the only value not equal to itself in JavaScript?
shortTitle: The only value not equal to itself
type: question
language: javascript
tags: [type,comparison]
cover: eagle
excerpt: Did you know there's a JavaScript value that's not equal to itself?
listed: true
dateModified: 2021-12-12
---
`NaN` (Not-a-Number) is the only JavaScript value not equal to itself when comparing with any of the comparison operators. `NaN` is often the result of meaningless or invalid math computations, so it doesn't make sense for two `NaN` values to be considered equal.
```js
const x = Math.sqrt(-1); // NaN
const y = 0 / 0; // NaN
x === y; // false
x === NaN; // false
Number.isNaN(x); // true
Number.isNaN(y); // true
isNaN(x); // true
isNan('hello'); // true
```
You can check for `NaN` values using the `Number.isNaN()` function. Note that this is different from the original , global `isNaN()`. Their difference lies in the fact that `isNaN()` forcefully converts its argument to a number, whereas `Number.isNaN()` doesn't. This is why `Number.isNaN()` is considered more robust and preferable in most cases.