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JavaScript isNaN() Function

Function Reference JavaScript Global Functions

Example

Check whether a number is an illegal number:

var a = isNaN(123) + "<br>";
var b = isNaN(-1.23) + "<br>";
var c = isNaN(5-2) + "<br>";
var d = isNaN(0) + "<br>";
var e = isNaN("Hello") + "<br>";
var f = isNaN("2005/12/12") + "<br>";

var res = a + b + c + d + e + f;

The result of res will be:

false
false
false
false
true
true

Try it yourself »

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.


Browser Support

Function
isNaN() Yes Yes Yes Yes Yes

Syntax

isNaN(value)

Parameter Values

Parameter Description
value Required. The value to be tested

Technical Details

Return Value: A Boolean. Returns true if the value is NaN, otherwise it returns false
JavaScript Version: 1.0

Function Reference JavaScript Global Functions

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