Core JavaScript 1.5 Guide:Predefined Functions:isNaN Function

From MDC

[edit] isNaN Function

The isNaN function evaluates an argument to determine if it is "NaN" (not a number). The syntax of isNaN is:

isNaN(testValue)

where testValue is the value you want to evaluate.

The parseFloat and parseInt functions return "NaN" when they evaluate a value that is not a number. isNaN returns true if passed "NaN," and false otherwise.

The following code evaluates floatValue to determine if it is a number and then calls a procedure accordingly:

floatValue=parseFloat(toFloat)

if (isNaN(floatValue)) {
   notFloat()
} else {
   isFloat()
}