Bootstrap 4导航栏切换按钮缩小时失效且不显示列表

Hey Franky, let's troubleshoot why your navbar toggler isn't popping up the menu when the browser window gets smaller. This is a super common issue with Bootstrap 4, and it almost always comes down to one of these easy-to-fix problems:

1. Double-Check Your Script Loading Order (and jQuery Version) #

Bootstrap's JavaScript relies on jQuery to work properly. While your code does load jQuery before Bootstrap JS (good call!), make sure you're using a jQuery version compatible with Bootstrap 4—that's jQuery 3.1.1 or newer. Older versions can break the toggler functionality.

If you're unsure, swap out your current jQuery script for a supported version (just make sure it's loaded before Bootstrap JS).

2. Verify Your Navbar HTML Structure #

Most of the time, the issue is incorrect markup. Bootstrap 4 requires a specific structure for the toggler and collapsible menu to hook up correctly. Here's the proper template to compare against your code:

<nav class="navbar navbar-expand-lg navbar-light bg-light">
  <!-- Brand/logo -->
  <a class="navbar-brand" href="#">Your Brand</a>

  <!-- Toggler button - must have these attributes -->
  <button class="navbar-toggler" type="button" 
          data-toggle="collapse" 
          data-target="#navbarMenu" 
          aria-controls="navbarMenu" 
          aria-expanded="false" 
          aria-label="Toggle navigation">
    <span class="navbar-toggler-icon"></span>
  </button>

  <!-- Collapsible menu container - ID must match data-target above -->
  <div class="collapse navbar-collapse" id="navbarMenu">
    <ul class="navbar-nav mr-auto">
      <li class="nav-item active">
        <a class="nav-link" href="#">Home</a>
      </li>
      <li class="nav-item">
        <a class="nav-link" href="#">About</a>
      </li>
      <li class="nav-item">
        <a class="nav-link" href="#">Contact</a>
      </li>
    </ul>
  </div>
</nav>

Key things to check in your code:

• The toggler button has data-toggle="collapse" and data-target="#yourMenuId"
• The collapsible menu container has an id that exactly matches the data-target value (case-sensitive!)
• All your nav links are inside the .collapse.navbar-collapse div

3. Check for File Loading Errors #

Open your browser's dev tools (F12) and go to the Network tab. Refresh the page and make sure:

• bootstrap.min.css and bootstrap.js are loading without 404 errors (double-check your file paths!)
• jQuery is loading successfully

If any of these files are missing, the toggler won't work because the required styles or scripts aren't there.

4. Rule Out Conflicting Code #

Sometimes custom CSS or other JavaScript can interfere with Bootstrap's functionality. Try temporarily removing any custom <style> blocks or extra scripts you have. If the toggler starts working, you'll know the issue is a conflict—then you can slowly add your code back in to find the culprit.

Give these steps a try, and your navbar toggler should start working as expected!

内容的提问来源于stack exchange，提问作者Franky Padilla