数组属于对象，对象有delete方法，可以删除数组元素。
var numbersArr = [1,2,3,4,5,6];
delete numbersArr[2];
//numbersArr结果为[1,2,undifined,4,5,6]
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数组提供splice方法
var numbersArr = [1,2,3,4,5,6];
numbersArr.splice(2,1);//第一个参数为数组序号，第二个参数为删除个数
//numbersArr结果为[1,2,4,5,6]，被删元素后面的元素序号都发生前移
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另外，splice方法还可以在任意位置插入元素：
let arr = [1,4,3,"a","c","e"];
arr.splice(2,0,"ok","fine",4,6)//[]
console.log(arr);//[1, 4, "ok", "fine", 4, 6, 3, "a", "c", "e"]
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