Html 引导导航栏未在mob视图中工作单击按钮时，下拉菜单未显示 免费试用！

这是我的导航栏，有人能告诉我错误是什么吗？为什么在mob视图中，当我点击按钮时，折叠菜单不显示

这是我正在使用的脚本，我正在使用bootstrap 4 cdn。有人能帮我吗？我已经检查了多篇关于堆栈溢出的帖子了

<nav class="navbar navbar-expand-lg mt-md-4 navbar-dark">
  <div class="container px-0">
    <a class="navbar-brand" href="#">
      <img src="./img/icon-assets/purple-tutor-logo.png" alt="" />
    </a>
    <button
      class="navbar-toggler custom-toggler"
      type="button"
      data-toggle="collapse"
      data-target="#navbarNav"
      aria-controls="navbarNav"
      aria-expanded="false"
      aria-label="Toggle navigation"
    >
      <span class="navbar-toggler-icon"></span>
    </button>
    <div class="collapse navbar-collapse" id="navbarNav">
      <div class="mr-auto"></div>
      <ul class="navbar-nav">
        <li class="nav-item" data-interval="3000">
          <a class="nav-link" href="#">Courses</a>
        </li>
        <li class="nav-item">
          <a class="nav-link" href="#">About Us</a>
        </li>
        <li class="nav-item">
          <a class="nav-link" href="#">How it Works</a>
        </li>
        <li class="nav-item">
          <a class="nav-link" href="#">FAQs</a>
        </li>
        <li class="nav-item">
          <a class="nav-link" href="#">School Registration</a>
        </li>
        <li class="nav-item">
          <a
            class="nav-link btn btn-lg btn-nav"
            href="https://study.purpletutor.com/register"
            >Get a FREE TRIAL!</a
          >
        </li>
      </ul>
    </div>
  </div>
</nav>

---

您的代码中没有错误，您只缺少用于在移动设备上使用下拉菜单的jquery，请将其添加到引导脚本之前，如下所示：

<script
  src="https://cdn.jsdelivr.net/npm/popper.js@1.16.1/dist/umd/popper.min.js"
  integrity="sha384-9/reFTGAW83EW2RDu2S0VKaIzap3H66lZH81PoYlFhbGU+6BZp6G7niu735Sk7lN"
  crossorigin="anonymous"
></script>
<script
  src="https://stackpath.bootstrapcdn.com/bootstrap/4.5.2/js/bootstrap.min.js"
  integrity="sha384-B4gt1jrGC7Jh4AgTPSdUtOBvfO8shuf57BaghqFfPlYxofvL8/KUEfYiJOMMV+rV"
  crossorigin="anonymous"
></script>

---

请删除您的答案，我需要删除此问题

<script src="https://code.jquery.com/jquery-3.5.1.slim.min.js" integrity="sha384-DfXdz2htPH0lsSSs5nCTpuj/zy4C+OGpamoFVy38MVBnE+IbbVYUew+OrCXaRkfj" crossorigin="anonymous"></script>
<script
  src="https://cdn.jsdelivr.net/npm/popper.js@1.16.1/dist/umd/popper.min.js"
  integrity="sha384-9/reFTGAW83EW2RDu2S0VKaIzap3H66lZH81PoYlFhbGU+6BZp6G7niu735Sk7lN"
  crossorigin="anonymous"
></script>
<script
  src="https://stackpath.bootstrapcdn.com/bootstrap/4.5.2/js/bootstrap.min.js"
  integrity="sha384-B4gt1jrGC7Jh4AgTPSdUtOBvfO8shuf57BaghqFfPlYxofvL8/KUEfYiJOMMV+rV"
  crossorigin="anonymous"
></script>