Javascript – Fragen zur Vererbung

Question

<code>function extend(Child,Parent){
var F=function(){};
F.prototype=Parent.prototype;
Child.prototype=new F();
Child.prototype.constructor=Child;
Child.uber=Parent.prototype;
}

function Shape(){}
Shape.prototype.name='Shape';
Shape.prototype.toString=function(){
return this.constructor.uber
    ?this.constructor.uber.toString()+', ' + this.name
    :this.name;
};

function TwoDShape(){}
extend(TwoDShape,Shape);
TwoDShape.prototype.name='2D shape';

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

var F=function(){};
extend(Triangle,TwoDShape);
Triangle.prototype.name='Triangle';
Triangle.prototype.getArea=function(){
return this.side*this.height/2;
};

var Shape=function(){};
var TwoDShape=function(){};
Shape.prototype.name='shape';
Shape.prototype.toString=function(){
return this.uber
?this.uber.toString()+', ' + this.name
:this.name;
};

extend(TwoDShape,Shape);
var td=new TwoDShape();

td.name;//"shape"
</code>

1. Warum heißt es, dass das Namensattribut weder ein Attribut der TwoDShape()-Instanz noch ihres Prototypobjekts ist, Unterobjekte aber dennoch durch Vererbung auf dieses Attribut zugreifen können?

Answer 1

因为子对象继承的是一整条原型链，而不是单个原型

Answer 2

挂载在原型链上的属性当然不是