Adobe 65036570 Scripting Guide - Page 97

ADOBE DIRECTOR 11.0 60 Scripting Dictionary • Instance variables • Instance methods • Class variables • Class methods Instance variables Instance variables are any variables (properties) that are defined in a constructor function and are copied into each object instance of that constructor. All object instances have their own copies of instance variables. This means that if there are five object instances of a Circle class, there are five copies of each instance variable defined in the class. Because each object instance has its own copy of an instance variable, each object instance can assign a unique value to an instance variable without modifying the values of other copies of the instance variable. You access instance variables directly from their containing object instances. The following example defines four instance variables-make, model, color, and speed-in a constructor function. These four instance variables are available directly from all object instances of the Car constructor: function Car(make, model, color) { // define a Car class this.make = make; this.model = model; this.color = color; this.speed = 0; } The following object instance objCar contains all four instance variables. Although a value for the instance variable speed is not passed to the Car constructor, objCar still has a speed property whose initial value is 0 because the speed variable is defined in the Car constructor. // objCar.make="Subaru", objCar.model="Forester", // objCar.color="silver", objCar.speed = 0 var objCar = new Car("Subaru", "Forester", "silver"); Instance methods Instance methods are any methods that are accessible through an object instance. Object instances do not have their own copies of instance methods. Instead, instance methods are first defined as functions, and then properties of the constructor function's prototype object are set to the function values. Instance methods use the keyword this in the body of the defining constructor function to refer to the object instance they are operating on. Although a given object instance does not have a copy of an instance method, you still access instance methods directly from their associated object instances. The following example defines a function named Car_increaseSpeed(). The function name is then assigned to the increaseSpeed property of the Car class's prototype object: // increase the speed of a Car function Car_increaseSpeed(x) { this.speed += x; return this.speed; } Car.prototype.increaseSpeed = Car_increaseSpeed; An object instance of Car could then access the increaseSpeed() method and assign its value to a variable by using the following syntax: var objCar = new Car("Subaru", "Forester", "silver"); var newSpeed = objCar.increaseSpeed(30);