导航栏Dropdown菜单在苹果触屏设备及部分浏览器中无法正常折叠

问题根源 #

iOS Safari的触摸事件机制有特殊性：默认状态下，非交互元素（如<body>、无交互属性的<div>）不会触发click事件，只有<button>、<a>这类原生可交互元素，或设置了cursor: pointer的元素，才能触发click。原代码中关闭下拉菜单的逻辑依赖window.onclick，但在iOS上点击屏幕空白区域时，这个click事件根本不会被触发，导致下拉菜单无法关闭。

修复方案 #

方案一：给<body>添加可交互样式 #

在CSS中为<body>添加cursor: pointer，让它能触发click事件：

body {
  background-color: white;
  cursor: pointer; /* 添加这一行 */
}

方案二：兼容触摸事件监听 #

修改JavaScript代码，同时监听click和touchstart事件，覆盖触摸设备的场景：

/* 切换下拉菜单显示/隐藏 */
function myFunction() {
  document.getElementById("myDropdown").classList.toggle("show");
}

/* 关闭下拉菜单的通用逻辑 */
function closeDropdown(e) {
  // 排除点击下拉按钮的情况
  if (!e.target.matches('.dropbtn')) {
    const myDropdown = document.getElementById("myDropdown");
    if (myDropdown.classList.contains('show')) {
      myDropdown.classList.remove('show');
    }
  }
}

// 同时绑定点击和触摸开始事件
window.addEventListener('click', closeDropdown);
window.addEventListener('touchstart', closeDropdown);

完整修复后的代码 #

<!DOCTYPE html>
<html>
<head>
<meta name="viewport" content="width=device-width, initial-scale=1">
<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/font-awesome/4.7.0/css/font-awesome.min.css">
<style>
.navbar {
  overflow: hidden;
  background-color: #333;
  font-family: Arial, Helvetica, sans-serif;
}

.navbar a {
  float: left;
  font-size: 16px;
  color: white;
  text-align: center;
  padding: 14px 16px;
  text-decoration: none;
}

.dropdown {
  float: left;
  overflow: hidden;
}

.dropdown .dropbtn {
  cursor: pointer;
  font-size: 16px;  
  border: none;
  outline: none;
  color: white;
  padding: 14px 16px;
  background-color: inherit;
  font-family: inherit;
  margin: 0;
}

.navbar a:hover, .dropdown:hover .dropbtn, .dropbtn:focus {
  background-color: red;
}

.dropdown-content {
  display: none;
  position: absolute;
  background-color: #f9f9f9;
  min-width: 160px;
  box-shadow: 0px 8px 16px 0px rgba(0,0,0,0.2);
  z-index: 1;
}

.dropdown-content a {
  float: none;
  color: black;
  padding: 12px 16px;
  text-decoration: none;
  display: block;
  text-align: left;
}

.dropdown-content a:hover {
  background-color: #ddd;
}

.show {
  display: block;
}

body {
  background-color: white;
  cursor: pointer; /* 新增样式 */
}
</style>
</head>
<body>

<div class="navbar">
  <a href="#home">Home</a>
  <a href="#news">News</a>
  <div class="dropdown">
  <button class="dropbtn" onclick="myFunction()">Dropdown
    <i class="fa fa-caret-down"></i>
  </button>
  <div class="dropdown-content" id="myDropdown">
    <a href="#">Link 1</a>
    <a href="#">Link 2</a>
    <a href="#">Link 3</a>
  </div>
  </div> 
</div>

<h3>Dropdown Menu inside a Navigation Bar</h3>
<p>Click on the "Dropdown" link to see the dropdown menu.</p>

<script>
function myFunction() {
  document.getElementById("myDropdown").classList.toggle("show");
}

function closeDropdown(e) {
  if (!e.target.matches('.dropbtn')) {
    const myDropdown = document.getElementById("myDropdown");
    if (myDropdown.classList.contains('show')) {
      myDropdown.classList.remove('show');
    }
  }
}

window.addEventListener('click', closeDropdown);
window.addEventListener('touchstart', closeDropdown);
</script>
</body>
</html>

内容的提问来源于stack exchange，提问作者dstonek