Adobe 65036570 Scripting Guide - Page 95

ADOBE DIRECTOR 11.0 58 Scripting Dictionary Object instances The most common way to create a new object instance is to use the new operator followed by the name of a constructor function. The following examples create new object instances: var objRandom = new Object(); // assigns a reference to an Object object var objString = new String(); // assigns a reference to a String object A constructor function can optionally define parameters that a new object instance passes to it to initialize the state of the object instance. If a constructor function does define parameters used during initialization of new object instances, the property values are initialized as follows: • If you pass values to the constructor function during initialization, the properties that received values are set to those values. • If you do not pass values to the constructor function during initialization, the properties that did not receive values are set to undefined. When you create new object instances, the keyword this is used in the body of the associated constructor function to refer to the new object instance. Therefore, a new object instance is initialized with all of the properties defined by using the this.propertyName syntax. In the following example, a Circle constructor function uses the keyword this to specify the names of three properties that will be associated with new object instances. The statement following the constructor initializes a new object instance by passing values to the constructor. These values are used as the initial values of the properties specified by the keyword this. // Circle constructor function function Circle(x, y, r) { this.xCoord = x; this.yCoord = y; this.radius = r; } // xCoord = 10, yCoord = 15, radius = 5 var objCircle = new Circle(10, 15, 5); Now that objCircle has been initialized, you can access its properties. Using the objCircle instance created previously, you could set some variables equal to the values of its properties. var theXCoord = objCircle.xCoord; // assigns the value 10 to theXCoord var theYCoord = objCircle.yCoord; // assigns the value 15 to theYCoord var theRadius = objCircle.radius; // assigns the value 5 to theRadius Note: For more information on using dot syntax to access properties and methods of an object, see "Scripting in dot syntax format" on page 42. It is considered good scripting practice to give new objects names that map to their functionality, and to name them by using lowercase letters, such as objRectangle or objCircle. You can also create an object instance by using object literal syntax, which eliminates the need for the new operator and a constructor function. You typically only use this technique when you need only one instance of an object that has not been defined in a constructor function. The following example creates an object instance with x = 1, y = 2, and radius = 2: var objSmallCircle = { x:1, y:2, radius:2 };