刪除指定下標數組元素 Array.prototype.del=function(index){     if(isNaN(index)||index>=this.length){       return false;     }     for(var i=0,n=0;i<this.length;i++){       if(this[i]!=this[index]){         this[n++]=this[i];       }     }     this.length-=1;   }; 刪除指定元素      Array.prototype.indexOf = function(val) {       for (var i = 0; i < this.length; i++) {         if (this[i] == val) return i;       }       return -1;     };     Array.prototype.remove = function(val) {       var index = this.indexOf(val);       if (index > -1) {         this.splice(index, 1);       }     };     function a(){       var arr = [1, 2, 3, 4, 5];     alert(arr.toString());     arr.remove(3);     alert(arr.toString());     }