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"]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"]