# NaN

The `NaN` property represents a value that is “not a number”. This special value results from an operation that could not be performed either because one of the operands was non-numeric (e.g., `"abc" / 4`), or because the result of the operation is non-numeric.

While this seems straightforward enough, there are a couple of somewhat surprising characteristics of `NaN` that can result in hair-pulling bugs if one is not aware of them.

For one thing, although `NaN` means “not a number”, its type is, believe it or not, `Number`:

```
console.log(typeof NaN === "number");  // logs "true"
```

Additionally, `NaN` compared to anything – even itself! – is false:

```
console.log(NaN === NaN);  // logs "false"
```

A *semi-reliable* way to test whether a number is equal to NaN is with the built-in function `isNaN()`, but even using [`isNaN()` is an imperfect solution](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/isNaN#Confusing_special-case_behavior).

A better solution would either be to use `value !== value`, which would *only* produce true if the value is equal to NaN. Also, ES6 offers a new [`Number.isNaN()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number/isNaN) function, which is a different and more reliable than the old global `isNaN()` function.

***Reference:*** [***Toptal Interview Questions*** ](https://www.toptal.com/javascript/interview-questions)