移动端视图下首页导航Toggle切换功能失效问题

故障现象 #

• 站点移动端适配开发接近完成，仅首页的汉堡菜单Toggle按钮点击无响应，无法正常展开/收起导航
• 其余二级页面、子菜单页面的Toggle切换功能运行完全正常

根因定位 #

故障核心原因是导航切换的JS逻辑存在硬编码缺陷：
原有JS通过严格匹配元素完整className值判断导航状态：

function myFunction() {
  var x = document.getElementById("myTopnav");
  if (x.className === "topnav") {
    x.className += " responsive";
  } else {
    x.className = "topnav";
  }
}

站点首页通常会给导航容器添加专属类名（比如首页高亮类、当前页标记类），此时#myTopnav的className值不是纯字符串topnav，判断逻辑会直接走else分支；如果首页的渲染逻辑会常驻维护这个专属类名，就会导致每次点击都永远无法追加responsive类触发展开样式，表现为点击无响应。
其他页面没有给导航容器添加额外类名，所以判断逻辑可正常运行，功能不受影响。

修复方案 #

将JS逻辑改为检测元素是否包含responsive类，而非硬匹配完整类名字符串，不会受其他额外类名干扰，兼容性更强，推荐使用classList原生API实现：

function myFunction() {
  var x = document.getElementById("myTopnav");
  x.classList.toggle("responsive");
}

如果需要兼容不支持classList的老旧浏览器，可以用字符串匹配的写法实现同等效果：

function myFunction() {
  var x = document.getElementById("myTopnav");
  if (x.className.indexOf("responsive") === -1) {
    x.className += " responsive";
  } else {
    x.className = x.className.replace(" responsive", "");
  }
}

附：原有相关代码 #

原有CSS样式 #

.topnav {
  overflow: hidden;
  background-color: #6EAD50;
}

.topnav a {
  float: left;
  display: block;
  color: #f2f2f2;
  text-align: center;
  padding: 14px 16px;
  text-decoration: none;
  font-size: 16px;
  letter-spacing: 2px;
}

.topnav a:visited {
  color: #ffffff;
}

.topnav .icon {
  display: none;
}

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

.dropdown .dropbtn {
  font-size: 16px;
  border: none;
  outline: none;
  color: white;
  padding: 17px 17px;
  background-color: inherit;
  font-family: inherit;
  margin: 0;
  letter-spacing: 2px;
}

.dropdown-content {
  display: none;
  position: absolute;
  background-color: #373538;
  min-width: 160px;
  box-shadow: 0px 8px 16px 0px rgba(0, 0, 0, 0.2);
  z-index: 1;
}

.dropdown-content a {
  float: none;
  color: #e3cc67fc;
  padding: 12px 16px;
  text-decoration: none;
  display: block;
  text-align: left;
}

.topnav a:hover,
.dropdown:hover .dropbtn {
  background-color: #e3cc67fc;
  color: white;
}

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

.dropdown:hover .dropdown-content {
  display: block;
}

@media screen and (max-width: 600px) {
  .topnav a:not(:first-child),
  .dropdown .dropbtn {
    display: none;
  }
  .topnav a.icon {
    float: right;
    display: block;
  }
}

@media screen and (max-width: 600px) {
  .topnav.responsive {
    position: relative;
  }
  .topnav.responsive .icon {
    position: absolute;
    right: 0;
    top: 0;
  }
  .topnav.responsive a {
    float: none;
    display: block;
    text-align: left;
  }
  .topnav.responsive .dropdown {
    float: none;
  }
  .topnav.responsive .dropdown-content {
    position: relative;
  }
  .topnav.responsive .dropdown .dropbtn {
    display: block;
    width: 100%;
    text-align: left;
  }
}

原有HTML结构 #

<div class="topnav" id="myTopnav">
  <a href="{$config{base_url}}">Home</a>

  <a href="{$config{base_url}}/help/index.html">Help</a>
  <div class="dropdown">
    <button class="dropbtn">Browse 
                                <i class="fa fa-caret-down"></i>
                            </button>
    <div class="dropdown-content">
      <a href="{$config{base_url}}/view/year/">Years</a>
      <a href="{$config{base_url}}/view/subjects/">Subjects</a>
      <a href="{$config{base_url}}/view/divisions/">Divisions</a>
      <a href="{$config{base_url}}/view/creators/">Authors</a>
      <a href="{$config{base_url}}/view/indexdbase/">Index Databases</a>
      <a href="{$config{base_url}}/view/type/">Document Type</a>
    </div>
  </div>
  <a href="{$config{base_url}}/information.html">About</a>
  <a href="{$config{base_url}}/policies.html">Policies</a>
  <a href="javascript:void(0);" style="font-size:15px;" class="icon" onclick="myFunction()">&#9776;</a>

</div>

内容的提问来源于stack exchange，提问作者Abid Fakhrealam