诸多问题的正方形继承矩形

Javascript代码  
Object.prototype.extend = function (Parent) {   
    this.prototype = new Parent();   
}   
Rectangle = function (width, height) {   
    this.width = width;   
    this.height = height;   
}   
Rectangle.prototype.area = function () {   
    return this.width * this.height;   
}   
Square = function (width) {   
    this.__proto__.width = width;   
    this.__proto__.height = width;   
    this.whoami = function () {   
        return "I am a Square.";   
    }   
}   
Square.extend(Rectangle);   
  
var s = new Square(5);   
document.writeln(s.area());  // The output is 25.   
document.writeln(s.whoami()); // The output is "I am a Square."  

Object.prototype.extend = function (Parent) {
    this.prototype = new Parent();
}
Rectangle = function (width, height) {
    this.width = width;
    this.height = height;
}
Rectangle.prototype.area = function () {
    return this.width * this.height;
}
Square = function (width) {
    this.__proto__.width = width;
    this.__proto__.height = width;
    this.whoami = function () {
        return "I am a Square.";
    }
}
Square.extend(Rectangle);

var s = new Square(5);
document.writeln(s.area());  // The output is 25.
document.writeln(s.whoami()); // The output is "I am a Square."


以上代码存在很多问题，不知你能说出几个？

this.__proto__啊……还真有人会在编程过程中用到这东西……

在prototype.method用this，还有this.__proto__。。。

不错..........

不错..........