JavaScript isNaN() Function (original) (raw)

Last Updated : 23 Jul, 2025

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 `

`

Output:

false true false true true false true

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

Supported Browsers:

• Chrome 1 and above
• Firefox 1 and above
• Edge 12 and above
• Opera 3 and above
• Safari 1 and above

We have a Cheat Sheet on Javascript where we covered all the important topics of Javascript to check those please go through Javascript Cheat Sheet-A Basic guide to JavaScript.