一段js，求解释

            (function(){

                if (!Function.prototype.bind) {

					alert(1);

                    Function.prototype.bind = function(obj){

						alert(2);

                        var owner = this, args = Array.prototype.slice.call(arguments), 

             				callobj = Array.prototype.shift.call(args);

                        return function(e){

							alert(1);

                            e = e || top.window.event || window.event;

                            owner.apply(callobj, args.concat([e]));

                        };

                    };

                }

            })();

------解决方案--------------------
 
(function(){
      if (!Function.prototype.bind) { //判断有没有加过bind属性
          alert(1);
          Function.prototype.bind = function(obj){
              alert(2);
              var owner = this, args = Array.prototype.slice.call(arguments),