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JavaScript isNaN() Function

Function Reference JavaScript Functions

Definition and Usage

The isNaN() function is used to check if a value is not a legal number, NaN (Not-a-Number).

Syntax

isNaN(value)

Parameter Description
value Required. The value to be tested

Example

Example

Check for NaN values:

<script type="text/javascript">

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 Functions

From http://www.w3schools.com (Copyright Refsnes Data)