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

JavaScript NaN Property

Number Object Reference JavaScript Number Object

Definition and Usage

The NaN property is a special value representing Not-a-Number. This property is used to indicate a value is not a legal number. A number object may be set to this value to indicate that it is not really a number.

Tip: Use the isNaN() global function to see if a value is an NaN value.

Syntax

Number.NaN

Example

Example

Use NaN to indicate that a value is not a number:

<script type="text/javascript">

var Month=30;

if (Month < 1 || Month > 12)
{
Month = Number.NaN;
}

document.write(Month);

</script>

The output of the code above will be:

Nan

Try it yourself »

Number Object Reference JavaScript Number Object

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