element UI中select 选择器如何增加全选选项

html 页面

js 在watch 监控 my_stars 变量

watch: {
   
    my_stars: function(val, oldval) {
      let newindex = val.indexOf("0"),
        oldindex = oldval.indexOf("0"); //获取val和oldval里all的索引,如果没有则返回-1
      //选择全选时，之前是没有全选状态
      if (newindex != -1 && oldindex == -1 && val.length > 0) {
        this.my_stars = ["0"];
        this.stars.forEach(v => {
          this.my_stars.push(v.number);
        });
        //选择全选时，之前是全选状态
      } else if (newindex == -1 && oldindex != -1 && val.length > 1) {
        this.my_stars = [];
        //选择 非全选 选项时，之前是全选状态
      } else if (
        newindex != -1 &&
        oldindex != -1 &&
        Math.abs(val.length - oldval.length) == 1
      ) {
        this.my_stars.shift("0");
        //选择 非全选 选项时，选择完了所有的星级级别
      } else if (
        newindex == -1 &&
        oldindex == -1 &&
        this.stars.length == val.length &&
        val.length > 0
      ) {
        this.my_stars = ["0"];
        this.stars.forEach(v => {
          this.my_stars.push(v.number);
        });
      }
    }
  },