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JavaScript isNaN() Function

Function Reference JavaScript Global Functions

Definition and Usage

The isNaN() function determines whether a value is an illegal number (Not-a-Number).

This function returns true if the value is NaN, and false if not.

Syntax

isNaN(value)

Parameter Description
value Required. The value to be tested


Browser Support

Internet Explorer Firefox Opera Google Chrome Safari

The isNaN() function is supported in all major browsers.


Example

Example

Check whether a number is an illegal number:

<script>

document.write(isNaN(123)+ "<br>");
document.write(isNaN(-1.23)+ "<br>");
document.write(isNaN(5-2)+ "<br>");
document.write(isNaN(0)+ "<br>");
document.write(isNaN("Hello")+ "<br>");
document.write(isNaN("2005/12/12")+ "<br>");

</script>

The output of the code above will be:

false
false
false
false
true
true

Try it yourself »


Function Reference JavaScript Global Functions

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