如何提醒Shape，TwoDShape类的名称？

Question

I have this Demo which execution alert and it is work well:

below the code.

var Shape = function(){};
var TwoDShape = function(){};
Shape.prototype.name = 'shape';
Shape.prototype.toString = function(){return this.name;};

alert('there is alert');​

when I add this line : extend(TwoDShape, Shape);

I can't to execution alert as you can see Demo

after this I add lines:

var my = new TwoDShape();
alert(my.toString());
alert(TwoDShape.prototype.name);
alert(my.hasOwnProperty('name'));

to alert the name of the class shape or TwoDShape but I can't successfull to display the class.name why ?

here is the full code:​

Answer 1

First, you do not have function extend() inside you code, so the code encounters error there and stopped running.

So I fixed it using jQuery $.extend() , or you can write the extend() yourself (see Jimmy's answer).

Secondly, if you want all Shape/TwoDShape instances have the class name to be accessible using toString() , you need to extend the prototype:

TwoDShape.prototype = $.extend(TwoDShape.prototype, Shape.prototype);

See the jsfiddle I created http://jsfiddle.net/4Bjjp/6/ on extending prototype

Answer 2

Your code break because extend function does not exist. You've to implement your own to make it work. Here is a simple implementation.

function extend(destination, source) {
  for (var key in source) {
    if(source.hasOwnProperty(key)) {
      destination[key] = source[key];
    }
  }

  return destination;
}