<script>
    var arr1 = ["red", "green", "blue"];
    arr1[2] = "pink"; //覆盖掉索引号2的值；
    console.log(arr1);
    arr1[3] = "black"; //输入没有占用的索引号会添加新元素
    console.log(arr1);
  </script>

新增数组元素  用修改索引号  追加数组元素