under——子对象访问父对象的方式

function Shape(){}
Shape.prototype.name=‘shape‘;
Shape.prototype.toString=function(){
    var result=[];
    if(this.constructor.under){
        result[result.length]=this.constructor.under.toString();
    }
    result[result.length]=this.name;
    return result.join(‘, ‘);
};

function TwoDShape(){}
var F=function(){}
F.prototype=Shape.prototype;
TwoDShape.prototype=new F();
TwoDShape.prototype.constructor=TwoDShape;
TwoDShape.uner=Shape.prorotype;
TwoDShape.prototype.name=‘2D shape‘;

function Triangle(side,height){
    this.side=side;
    this.height=height;

}

var F =function(){}
F.prototype=TwoDShape.prototype;