FLASH® LITE™ 2.x - Adobe Help and Support

Example
In the following example, an object has two internal methods, setQuantity() and
getQuantity(). A property, bookcount, can be used to invoke these methods when it is
either set or retrieved. A third internal method, getTitle(), returns a read-only value that is
associated with the property bookname. When a script retrieves the value of
myBook.bookcount, the ActionScript interpreter automatically invokes
myBook.getQuantity(). When a script modifies the value of myBook.bookcount, the
interpreter invokes myObject.setQuantity(). The bookname property does not specify a
set function, so attempts to modify bookname are ignored.
function Book() {
this.setQuantity = function(numBooks:Number):Void {
this.books = numBooks;
};
this.getQuantity = function():Number {
return this.books;
};
this.getTitle = function():String {
return "Catcher in the Rye";
};
this.addProperty("bookcount", this.getQuantity, this.setQuantity);
this.addProperty("bookname", this.getTitle, null);
}
var myBook = new Book();
myBook.bookcount = 5;
trace("You ordered "+myBook.bookcount+" copies of "+myBook.bookname);
// output: You ordered 5 copies of Catcher in the Rye
The previous example works, but the properties bookcount and bookname are added to every
instance of the Book object, which requires having two properties for every instance of the
object. If there are many properties, such as bookcount and bookname, in a class, they could
consume a great deal of memory. Instead, you can add the properties to Book.prototype so
that the bookcount and bookname properties exist only in one place. The effect, however, is
the same as that of the code in the example that added bookcount and bookname directly to
every instance. If an attempt is made to access either property in a Book instance, the
property's absence will cause the prototype chain to be ascended until the versions defined in
Book.prototype are encountered. The following example shows how to add the properties to
Book.prototype:
function Book() {}
Book.prototype.setQuantity = function(numBooks:Number):Void {
this.books = numBooks;
};
Book.prototype.getQuantity = function():Number {
return this.books;
};
522 ActionScript classes