使用splice方法,index为插入的位置
array.splice(index, 0, 元素)
例如,["张三","李四","王五"]
在"李四"前面插入,‘张四’
array = ["张三","李四","王五"] (3) ["张三", "李四", "王五"] array.splice(1,0,"张四") []length: 0__proto__: Array(0) array (4) ["张三", "张四", "李四", "王五"]