In this article, we will learn what does NaN mean in JavaScript programming with code example.

In JavaScript, `NaN`

stands for “Not a Number.” It’s a special value that represents the result of an undefined or unrepresentable mathematical operation, such as the square root of a negative number, or the result of trying to parse an invalid number from a string.

For example, the following code will return `NaN`

:

```
parseFloat("not a number"); // NaN
```

`Math.sqrt(-1); // NaN`

It’s important to note that `NaN`

is a unique value in JavaScript, meaning that `NaN`

is not equal to any other value, including itself. So the following comparison is not working as it should

```
if (value === NaN) {
// This block will not execute if value is NaN
}
```

To check if a value is NaN you can use the function `isNaN(value)`

```
if (isNaN(value)) {
// this block will execute if value is NaN
}
```

Another way to check NaN values is the `Number.isNaN(value)`

it introduced in ES6 that is more accurate than the global `isNaN()`

```
if (Number.isNaN(value)) {
// this block will execute if value is NaN
}
```

It’s important to note that in Javascript NaN is of type number, it’s a number but a special one, that you should take care when working with it.

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