isNaN Function (JavaScript)

Returns a Boolean value that indicates whether a value is the reserved value NaN (not a number).

Syntax

isNaN(numValue)   

Return Value

true if the value converted to the Number type is the NaN, otherwise false.

Remarks

The required numValue is the value to be tested against NaN.

You typically use this method to test return values from the parseInt and parseFloat methods.

Alternatively, a variable that contains NaN or another value could be compared to itself. If it compares as unequal, it is NaN. This is because NaN is the only value that is not equal to itself.

Requirements

Supported in the following document modes: Quirks, Internet Explorer 6 standards, Internet Explorer 7 standards, Internet Explorer 8 standards, Internet Explorer 9 standards, Internet Explorer 10 standards, Internet Explorer 11 standards. Also supported in Store apps (Windows 8 and Windows Phone 8.1). See Version Information.

Applies To: Global Object

Example

// Returns false.  
isNaN(100);  

// Returns false.  
isNaN("100");  

// Returns true.  
isNaN("ABC");  

// Returns true.  
isNaN("10C");  

// Returns true.  
isNaN("abc123");  

// Returns true.  
isNaN(Math.sqrt(-1));           

See Also

isFinite Function
NaN Constant
parseFloat Function
parseInt Function