JavaScript isNaN() Function

Last Updated : 11 Jun, 2026

The JavaScript isNaN() Function is used to check whether a given value is an illegal number or not. It returns true if the value is a NaN else returns false. It is different from the Number.isNaN() Method.

Syntax:

isNaN( value )

Parameter Values: This method accepts a single parameter as mentioned above and described below: 

  • value: It is a required value passed in the isNaN() function.

Return Value: It returns a Boolean value i.e. returns true if the value is NaN else returns false.

Example: In this example, we will check various values for isNan() and the output will be in boolean format.

JavaScript 
<script>
    console.log(isNaN(12));
    console.log(isNaN(0 / 0));
    console.log(isNaN(12.3));
    console.log(isNaN("Geeks"));
    console.log(isNaN("13/12/2020"));
    console.log(isNaN(-46));
    console.log(isNaN(NaN));
</script>

We have a complete list of Javascript Function methods, to check those please go through this Javascript Function Complete reference article.

Comment

Explore