javascript数组赋值操作

1 ......
2 
3             var _len = arr1.length;
4             while (_len) {
5                 arr2[--_len] = arr1[_len];
6             }
7 
8 ......

1 function assignment2(arr1, arr2) {
2             for (var i = 0,_len = arr1.length; i < _len; i++) {
3                 arr2[i] = arr1[i];
4             }
5         }

1 function consoleRunTime() {
2             this.ti = 0;
3             this.start = function () {
4                 this.ti = new Date().getTime();
5             }
6             this.end = function () {
7                 console.log(new Date().getTime() - this.ti);
8             }
9         }