js 实现类式继承

1. /* Simple JavaScript Inheritance
2.  * By John Resig http://ejohn.org/
3.  * MIT Licensed.
4.  */
5. // Inspired by base2 and Prototype
6. (function(){
7.   var initializing = false, fnTest = /xyz/.test(function(){xyz;}) ? /\b_super\b/ : /.*/;
8.  
9.   // The base Class implementation (does nothing)
10.   this.Class = function(){};
11.  
12.   // Create a new Class that inherits from this class
13.   Class.extend = function(prop) {
14.     var _super = this.prototype;
15.    
16.     // Instantiate a base class (but only create the instance,
17.     // don't run the init constructor)
18.     initializing = true;
19.     var prototype = new this();
20.     initializing = false;
21.    
22.     // Copy the properties over onto the new prototype
23.     for (var name in prop) {
24.       // Check if we're overwriting an existing function
25.       prototype[name] = typeof prop[name] == "function" &&
26.         typeof _super[name] == "function" && fnTest.test(prop[name]) ?
27.         (function(name, fn){
28.           return function() {
29.             var tmp = this._super;
30.            
31.             // Add a new ._super() method that is the same method
32.             // but on the super-class
33.             this._super = _super[name];
34.            
35.             // The method only need to be bound temporarily, so we
36.             // remove it when we're done executing
37.             var ret = fn.apply(this, arguments);        
38.             this._super = tmp;
39.            
40.             return ret;
41.           };
42.         })(name, prop[name]) :
43.         prop[name];
44.     }
45.    
46.     // The dummy class constructor
47.     function Class() {
48.       // All construction is actually done in the init method
49.       if ( !initializing && this.init )
50.         this.init.apply(this, arguments);
51.     }
52.    
53.     // Populate our constructed prototype object
54.     Class.prototype = prototype;
55.    
56.     // Enforce the constructor to be what we expect
57.     Class.prototype.constructor = Class;
58.  
59.     // And make this class extendable
60.     Class.extend = arguments.callee;
61.    
62.     return Class;
63.   };
64. })();