splice() 方法向/从数组中添加/删除项目，然后返回被删除的项目

删除位于 index 2 的元素，并添加一个新元素来替代被删除的元素：

<script type="text/javascript">

       var arr = new Array(6)
       arr[0] = "George"
       arr[1] = "John"
       arr[2] = "Thomas"
       arr[3] = "James"
       arr[4] = "Adrew"
       arr[5] = "Martin"

       document.write(arr + "<br />")
       arr.splice(2,1,"William")
       document.write(arr)

</script><scr