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isNaN Function (JavaScript)

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

isNaN(numValue) 

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

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.

Supported in the following document modes: Quirks, Internet Explorer 6 standards, Internet Explorer 7 standards, Internet Explorer 8 standards, Internet Explorer 9 standards. See Version Information.

Applies To: Global Object (JavaScript)

isNaN(100);                   //Returns false
isNaN("100");                 //Returns false
isNaN("ABC");                 //Returns true
isNaN("10C");                 //Returns true
isNaN(Math.sqrt(-1));         //Returns true

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