ECMA5数组的新方法forEach（）模仿实现

 1       var o = {
 2             forEach: function (callback) {
 3                // alert(this.length);
 4                 for (var i = 0, len = this.length; i < len; i++) {
 5                     callback && callback(this[i], i, this);
 6                 }
 7             },
 8             get length(){
 9                 var sum=0;
10                 for(var n in this) {
11                     sum+=1;
12                 }
13                 return sum;
14             }
15 
16         };
17         Object.defineProperty(o,"length",{enumerable:false});
18         Object.defineProperty(o,"forEach",{enumerable:false});
19         o[0] = 0;
20         o[1] = 1;
21         o[2] = 2;
22 
23         o.forEach(function(v,i,arr){
24             arr[i]=v+1;
25             console.log(arr[i]+"callback");
26         });