ActionScript for Flash MX: The Definitive Guide, Second Edition

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isNaN() Global Function

equality test for the special NaN value

Flash 5

isNaN(value)

Arguments

value The expression to test.

Returns

The Boolean true if value is the special numeric value NaN; otherwise, false.

Description

To test whether or not a value is equal to the special numeric value NaN, we must use the

isNaN( ) function, because

NaN does not test equal to itself in an ordinary equality test. For

example, the expression:

NaN = = NaN;

yields the value false. The isNaN( ) function is often used to check whether a mathemat-

ical error (such as zero divided by itself) has occurred, or whether converting a value to a

legitimate number has failed. Because isNaN( ) returns

true when the expression is not a

valid numeric expression, you’ll often use the logical NOT operator (!) along with isNaN( )

(i.e., something that is not not-a-number is a number). Note that 0/0 yields

NaN, but any

positive number divided by 0 yields

Infinity, and any negative number divided by 0 yields

–Infinity.

Example

// Set a value

var x = "test123";

// Check if x is a legitimate number before using it is in a math expression. This

// is a handy for user input in text fields, which are always treated as strings.

if (!isNaN(parseFloat(x))) {

var y = parseFloat(x) * 2;

}

See Also ...