MACROMEDIA FLASH MX, Reference

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340 Chapter 2: ActionScript Language Reference
isNaN()
Availability
Flash Player 5.
Usage
isNaN( expression:Object ) : Boolean
Parameters
expression
A Boolean, variable, or other expression to be evaluated.
Returns
A Boolean value.
Description
Function; evaluates the parameter and returns
true
if the value is
NaN
(not a number). This
function is useful for checking whether a mathematical expression evaluates successfully to a
number.
Example
The following code illustrates return values for the
isNaN()
function:
trace( isNaN("Tree") );
// returns true
trace( isNaN(56) );
// returns false
trace( isNaN(Number.POSITIVE_INFINITY) )
// returns false
The following example shows how you can use
isNAN()
to check whether a mathematical
expression contains an error:
var dividend:Number;
var divisor:Number;
divisor = 1;
trace( isNaN(dividend/divisor) );
// output: true
// The output is true because the variable dividend is undefined.
// Do not use isNAN() to check for division by 0 because it will return false.
// A positive number divided by 0 equals Infinity (Number.POSITIVE_INFINITY).
// A negative number divided by 0 equals -Infinity (Number.NEGATIVE_INFINITY).
See also
NaN , Number.NaN
CHAPTER 2
ActionScript Language Reference