Professional JavaScript For Web Developers

Inheritance
Polygon.prototype.getArea = function () {
return 0;
};
}
}
Next, rewrite the Triangle class, which is the first taste of real inheritance in this example:
_classes.registerClass(“Triangle”, “Polygon”);
function Triangle(iBase, iHeight) {
_classes.defineClass(“Triangle”, prototypeFunction);
this.init(iBase,iHeight);
function prototypeFunction() {
Triangle.prototype.init = function(iBase, iHeight) {
this.parentMethod(“init”, 3);
this.base = iBase;
this.height = iHeight;
};
}
Triangle.prototype.getArea = function () {
return 0.5 * this.base * this.height;
};
}
Note the registerClass() call just before the constructor, where the inheritance relationship is set up.
Also, the first line of the init() method calls the superclass (Polygon) init() with an argument of 3,
which sets the sides property to 3. Other than that, the init() method is very similar: a simple constructor,
assigning the base and height.
The Rectangle class ends up looking very similar to Triangle:
_classes.registerClass(“Rectangle”, “Polygon”);
function Rectangle(iLength, iWidth) {
_classes.defineClass(“Rectangle”, prototypeFunction);
this.init(iLength, iWidth);
function prototypeFunction() {
Rectangle.prototype.init = function(iLength, iWidth) {
this.parentMethod(“init”, 4);
this.length = iLength;
this.width = iWidth;
}
123