关于子对象访问父对象的方式，看不明白第二步了，求大神解答下，多谢O(∩_∩)O

Question

function Shape(){}Shape.prototype.name="shape";Shape.prototype.toString=function(){    var const = this.constructor;    return  const.uber? this.const.uber.toString()+","+this.name:this.name;}function TwoDShape(){}var F=function(){};F.prototype=Shape.prototype;TwoDShape.prototype=new F();TwoDShape.prototype.constructor=TwoDShape;TwoDShape.uber=Shape.prototype;TwoDShape.prototype.name="2D shape";function Triangle(side,height) {    this.side=side;    this.height=height;}var F=function(){};F.prototype=TwoDShape.prototype;Triangle.prototype=new F();Triangle.prototype.constructor=Triangle;Triangle.uber=TwoDShape.prototype;Triangle.prototype.name="Triangle";Triangle.prototype.getArea=function(){    return this.side*this.height/2;};var my=new Triangle(5,10);my.toString();my没有tostring方法，不断的向上找，找到shape的tostring方法，输出的第一个为this.const.uber.toString+，Triangle，接着就看不明白了，const里面有个this，前面还有个this，（这个this不多余么？）有没有能把完整的过程解读下的大神，小弟跪谢了/(ㄒoㄒ)/~~