二、JavaScript 对象继承

  JavaScript 对象继承
    几何形状结构继承图

Polygon = function(iSides) { //多边形
	this.sides = iSides;
}
Polygon.prototype = { 
	getArea : function() { return 0; }
}

Triangle = function(iBase, iHeight) { //三角形
	Polygon.call(this, 3);
	this.base = iBase;
	this.height = iHeight;
}
Triangle.prototype = new Polygon();
Triangle.prototype = { 
	getArea : function() {
		return 0.5 * this.base * this.height;
	}
}

Rectangle = function(iLength, iWidth) { //矩形
	Polygon.call(this, 4);
	this.length = iLength;
	this.width = iWidth;
}
Rectangle.prototype = new Polygon();
Rectangle.prototype = {
	getArea : function() {
		return this.length * this.width;
	}
}