ActionScript for Flash MX: The Definitive Guide, Second Edition

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

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Chapter 5: Operators

When used as the left-hand operand of an assignment operator, the dot operator is

used to set a new value for a property:

var ball = new Object();

ball.radius = 150;

ball.xVelocity = 10;

When used anywhere else, a dot operation returns the value of the named object

property:

diameter = ball.radius * 2;

newX = ball.xPosition + ball.xVelocity;

The dot operator is also used to invoke object methods (functions stored in proper-

ties), as follows:

intro_mc.gotoAndPlay("beginMovie");

See Chapters 12 and 13 for details on the dot operator.

The Conditional Operator

The conditional operator is a syntactic convenience that lets us succinctly represent a

simple conditional statement. This operator takes three operands, in the form:

condition ? result_if_true : result_if_false;

When a conditional operation is executed, the first operand (condition) is evalu-

ated. If

condition is true or can be converted to true, the value of the second oper-

and (

result_if_true) is returned. Otherwise, the value of the third operand

(

result_if_false) is returned. See Chapter 7 for details on the conditional operator.

The instanceof Operator

The instanceof operator, added in Flash MX, checks whether an object is an instance

of a given class (or one of the class’s subclasses). It takes the form: