# isNaN JavaScript function | Check value is NaN(Not a Number)

The isNaN() Function used to determine whether the passed value is NaN(Not a Number)/illegal number in JavaScript. The global isNaN() function, converts the tested (given) value to a Number, then tests it.

### Syntax

``isNaN(value)``

### Parameter Values

The value which is to be tested for NaN.

### Return Value

This function returns true if the value equates to NaN else it returns false.

## Examples of isNaN() JavaScript function

Let’s see the different example code of isNaN() function.

### Pass the number as Parameter

``````<!DOCTYPE html>
<html>

<body>
<script type="text/javascript">
var num = 700;
document.write("Output : " + isNaN(num));
</script>

</body>

</html> ``````

## Equation resulting in the infinite value

``````<!DOCTYPE html>
<html>

<body>
<script type="text/javascript">
var num=0/0;
document.write("Output : " + isNaN(num));
</script>

</body>

</html> ``````

Output : true

### Pass the string as a parameter value

``````<script type="text/javascript">
var test='hello';
document.write("Output : " + isNaN(test));
</script>``````

Output : false

### Pass NaN

``````<!DOCTYPE html>
<html>

<body>
<script type="text/javascript">
var check=NaN;
document.write("Output : " + isNaN(check));
</script>

</body>

</html> ``````

Output : ture

### Q: How to remove NaN error in JavaScript?

Answer: You can use if conditions with isNaN() function to remove Nan error:

Note: Number.isNaN() doesn’t convert the values to a Number.

``````<!DOCTYPE html>
<html>

<body>
<script>
num = NaN;
if(isNaN(num)) num = 0;
</script>

</body>

</html> ``````

### Q: What does mean number.isnan(value) is not a function?

Answer: `Number.isNaN(x)` checks if x is directly evaluated to `NaN` or not.

The key difference between the two is that the global `isNaN(x)` the function performs a conversion of the parameter `x` to a number.

### Q: Difference between isNaN and Number.isNaN in javascript?

Answer: Here is differentiations:-

• `isNaN` converts the argument to a `Number` and returns true if the resulting value is `NaN`.
• `Number.isNaN` does not convert the argument; it returns true when the argument is a `Number` and is `NaN`.

Do comment if you have any questions and suggestions on this tutorial.

Note: The All JS Examples codes are tested on the Safari browser (Version 12.0.2) and Chrome.
OS: macOS 10.14 Mojave
Code: HTML 5 Version