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JavaScript isNaN() Function

Function Reference JavaScript Global Functions

Example

Check whether a value is NaN:

isNaN(123) //false
isNaN(-1.23) //false
isNaN(5-2) //false
isNaN(0) //false
isNaN('123') //false
isNaN('Hello') //true
isNaN('2005/12/12') //true
isNaN('') //false
isNaN(true) //false
isNaN(undefined) //true
isNaN('NaN') //true
isNaN(NaN) //true
isNaN(0 / 0) //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 equates to NaN. Otherwise it returns false.

This function is different from the Number specific Number.isNaN() method.

 The global isNaN() function, converts the tested value to a Number, then tests it.

Number.isNan() does not convert the values to a Number, and will not return true for any value that is not of the type Number.


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