注意点
 document.addEventListener("click", e => {
      if (!this.overMark && this.showArrow) {
        let el = e.target;
        while (el) {
          if (el.id == "menu-box") {
            return;
          }
          el = el.parentNode;
        }
        this.showArrow = false;
      }
    });
this.overMark跟this.showArrow就是一个额外判断,满足条件时才去循环查找父级id,直至匹配原文:https://www.cnblogs.com/ybchen292/p/14626379.html