for循环中in和of区别

代码：

<script>
      //数组遍历
      let arr = ["a", "b", "c"];
      arr[3] = "d";
      for (let item in arr) {
        console.log(item);
      }
      //结果 0 1 2 3
      for (let item of arr) {
        console.log(item);
      }
      //结果是a b c d


      //对象遍历
      let obj = { a: "小明", b: "小红", c: "小兰" };
      obj.d = "小王";
      for (let item in obj) {
        console.log(item);
      }
      //获得key值: a b c d



      for (let item of obj) {
        //对象不能使用of
        console.log(item);
      }
      //Uncaught TypeError: obj is not iterable
    </script>

in用来循环对象并获得key值，循环数组获得索引

of用来循环数组得到数组中的值