Core JavaScript 1.5 Reference:Global Functions:isNaN
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[edit] Summary
Core Function
Evaluates an argument to determine if it is not a number.
[edit] Syntax
isNaN(testValue)
[edit] Parameters
-
testValue - The value you want to evaluate.
[edit] Description
isNaN is a top-level function and is not associated with any object.
isNaN attempts to convert the passed parameter to a number. If the parameter can't be converted, it returns true; otherwise, it returns false.
This function is useful because the value NaN cannot be meaningfully tested with the equality operators. x == NaN and x === NaN are always false, regardless of what x is, even if x is NaN. For example, both 1 == NaN and NaN == NaN return false.
[edit] Examples
isNaN(NaN) //returns true
isNaN("string") //returns true
isNaN("12") //returns false
isNaN(12) //returns false