JavaScript实现HTML导航栏下拉菜单：悬浮显示与防Bug处理

//获取需要悬浮的对象
  let show = document.getElementById("show");
  //获取被隐藏的菜单
  let menu = document.getElementById("menu");

//给show添加鼠标悬浮事件
  show.onmouseover = function(){
     //改变菜单的内联样式display为block，菜单显示
     menu.style.display = "block";
  }

show.onmouseout = function(){
   //获取菜单栏的坐标值
   let menux = menu.offsetLeft;
   let menuy = menu.offsetTop;
   let menuX = menu.offsetLeft+menu.offsetWidth;
   let menuY = menu.offsetTop+menu.offsetHeight;

   //获取鼠标的坐标值
   let event = window.event;
   let mouseX = event.clientX;
   let mouseY = event.clientY;

   if(mouseX<menux || mouseX>menuX || mouseY<menuY || mouseY>menuY){
     menu.style.display = "none";
   }
 }

//分别给menu对象绑定鼠标悬浮和鼠标离开事件
menu.onmouseover = function(){
   menu.style.display = "block";
}
menu.onmouseleave = function(){
   menu.style.display = "none";
}

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <script>
    window.onload = function(){
      //获取需要悬浮的对象
      let show = document.getElementById("show");
      //获取被隐藏的菜单
      let menu = document.getElementById("menu");

      //给show添加鼠标悬浮事件
      show.onmouseover = function(){
        //改变菜单的内联样式display为block
        menu.style.display = "block";
      }

      //
      show.onmouseout = function(){
        //获取菜单栏的坐标值
        let menux = menu.offsetLeft;
        let menuy = menu.offsetTop;
        let menuX = menu.offsetLeft+menu.offsetWidth;
        let menuY = menu.offsetTop+menu.offsetHeight;

        //获取鼠标的坐标值
        let event = window.event;
        let mouseX = event.clientX;
        let mouseY = event.clientY;

        if(mouseX<menux || mouseX>menuX || mouseY<menuY || mouseY>menuY){
          menu.style.display = "none";
        }
      }

      //分别给menu对象绑定鼠标悬浮和鼠标离开事件
      menu.onmouseover = function(){
        menu.style.display = "block";
      }
      menu.onmouseleave = function(){
        menu.style.display = "none";
      }
    }
  </script>
  <style>
    *{
      margin: 0;
      padding: 0;
    }
    li{
      list-style: none;
    }
    #show {
      margin-top: 10px;
      margin-left: 10px;
      width: 50px;
      height: 30px;
      border: 1px solid #ccc;
      background-color: pink;
    }
    #menu{
      display: none;
      margin-left: 10px;
      width: 50px;
      border: 1px solid #ccc;
      background: rgba(0, 0, 0, 0.6);
    }
    #menu a{
      color: #fff;
      text-decoration: none;
    }
  </style>
</head>
<body>
  <div id="box">
    <div id="show"><a href="#">Gorho</a></div>
    <ul id="menu">
      <li><a href="#">选项一</a></li>
      <li><a href="#">选项二</a></li>
      <li><a href="#">选项三</a></li>
    </ul>
  </div>
</body>
</html>