数组方法的封装

var arr = [1, 5, 9, 4, 5, 6, 7, 8];
       Array.prototype.myslice =  () {
           var newArr = [];
           // 当有一个参数的时候
           if (arguments.length === 1) {
               var start = arguments[0] < 0 ? this.length + arguments[0] : arguments[0];
               for (var i = start; i < this.length; i++) {
                   newArr.push(this[i]);
               }
           } else if (arguments.length == 2) {  // 两个参数的时候
               var start = arguments[0] < 0 ? this.length + arguments[0] : arguments[0];
               var end = arguments[1] < 0 ? this.length + arguments[1] : arguments[1];
               for (var i = start; i < end; i++) {
                   newArr.push(this[i]);
               }
               if (arguments[0] > arguments[1]) {
                   for (var i = start; i > end; i--) {
                       newArr.push(this[i]);
                   }
               }
           }
           return newArr;
       }

var arr1 = [1, 2, 3, 4, 5, 6, 7];
   Array.prototype.mypush =  () {
       var argLength = arguments.length;
       var arrLength = this.length;    
       for (var i = arrLength, j = 0; i < arrLength + argLength; i++ , j++) {
           this[i] = arguments[j];
       }
       return this;
   }
   arr1.mypush(1, 2);