delete Array'item

原文链接：http://caibaojian.com/js-splice-element.html

2：delete       ·

delete删除掉数组中的元素后，会把该下标出的值置为undefined,数组的长度不会变

//code from http://caibaojian.com/js-splice-element.html
var arr = ['a','b','c','d'];
delete arr[1];
arr;  
//["a", undefined × 1, "c", "d"] 中间出现两个逗号，数组长度不变，有一项为undefined