ActionScript for Flash MX: The Definitive Guide, Second Edition

This is the Title of the Book, eMatter Edition

Copyright © 2007 O’Reilly & Associates, Inc. All rights reserved.

The Logical Operators

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The technical behavior of the logical AND operator is quite similar to that of the log-

ical OR operator. First, operand1 is converted to a Boolean. If the result of that con-

version is

false, the value of operand1 is returned. If the result of that conversion is

true, the value of operand2 is returned.

If the first operand in a logical AND operation resolves to

false, it is unnecessary,

and therefore inefficient, to evaluate the second operand. Therefore, ActionScript

evaluates the second operand only if the first operand resolves to

true. This fact is

useful in cases in which you don’t want to resolve the second operand unless the first

operand resolves to

true. In this example, we perform the division only if the divisor

is nonzero:

if (numItems != 0 && total / numItems > 3) {

trace("You've averaged more than 3 dollars per transaction");

}

Logical NOT

The logical NOT operator (!) returns the Boolean opposite of its single operand. It

takes the general form:

!operand

where operand can be any legal expression. If operand is true, logical NOT returns

false.Ifoperand is false, logical NOT returns true.Ifoperand is not a Boolean, its

value is converted to a Boolean for the sake of the operation and its opposite is

returned.

Like the does-not-equal operator (

!=), the