Javascript 为什么我的引导4导航栏下拉菜单不能工作？_Javascript_Bootstrap 4_Navbar

Javascript 为什么我的引导4导航栏下拉菜单不能工作？

javascript bootstrap-4

Javascript 为什么我的引导4导航栏下拉菜单不能工作？,javascript,bootstrap-4,navbar,Javascript,Bootstrap 4,Navbar,我似乎不明白。jQuery在引导javascript之前被引用，html代码看起来也不错。有什么想法吗导航：在文件底部的javascript引用之前： <script src="https://code.jquery.com/jquery-3.4.1.min.js"></script> <script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.14.7/umd/popper

我似乎不明白。jQuery在引导javascript之前被引用，html代码看起来也不错。有什么想法吗

导航：

在文件底部的javascript引用之前：

      <script src="https://code.jquery.com/jquery-3.4.1.min.js"></script>
    <script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.14.7/umd/popper.min.js" integrity="sha384-UO2eT0CpHqdSJQ6hJty5KVphtPhzWj9WO1clHTMGa3JDZwrnQq4sF86dIHNDz0W1" crossorigin="anonymous"></script>
    <script src="https://stackpath.bootstrapcdn.com/bootstrap/4.3.1/js/bootstrap.min.js" integrity="sha384-JjSmVgyd0p3pXB1rRibZUAYoIIy6OrQ6VrjIEaFf/nJGzIxFDsf4x0xIM+B07jRM" crossorigin="anonymous"></script>
  </body>
</html>

您的代码片段是一个PHP脚本；您应该调试生成的HTML，而不是包含PHP的代码

删除PHP部件并在页眉部分包含Bootstrap 4 CSS文件后：

<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0/css/bootstrap.min.css" integrity="sha384-Gn5384xqQ1aoWXA+058RXPxPg6fy4IWvTNh0E263XmFcJlSAwiGgFAW/dAiS6JXm" crossorigin="anonymous">

你的页面完全正常

最终工作HTML：

<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8" />
    <link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0/css/bootstrap.min.css" integrity="sha384-Gn5384xqQ1aoWXA+058RXPxPg6fy4IWvTNh0E263XmFcJlSAwiGgFAW/dAiS6JXm" crossorigin="anonymous">
</head>
<body>
    <nav class="navbar navbar-expand-lg navbar-light bg-white" style="border-bottom: 2px solid #ccc;">
    <div class="container">
        <a class="navbar-brand" href="#">
            <img src="assets/img/logo.png" alt="CraftZealous"/>
        </a>
        <button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#navbarSupportedContent" aria-controls="navbarSupportedContent" aria-expanded="false" aria-label="Toggle navigation">
            <span class="navbar-toggler-icon"></span>
        </button>

    <div class="collapse navbar-collapse" id="navbarSupportedContent">
        <ul class="navbar-nav mr-auto">
            <li class="nav-item">
                <a class="nav-link text-info" href="#" style="font-weight: 700;">HOME</a>
            </li>
            <li class="nav-item">
                <a class="nav-link text-dark" href="#faq">HELP &amp; FAQ</a>    
            </li>
            <li class="nav-item">
                <a class="nav-link text-dark" href="#community">COMMUNITY</a>
            </li>
            <li class="nav-item">
                <a class="nav-link text-dark" href="#">NEWS</a>
            </li>
        </ul>
        <ul class="nav navbar-nav ml-auto">
            <li class="nav-item dropdown">
                <a href="#" class="nav-link dropdown-toggle text-danger" id="dropdown01" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false" style="text-transform:uppercase;">SC</a>
                <div class="dropdown-menu" aria-labelledby="dropdown01">
                  <a class="dropdown-item" href="#">Profile</a>
                  <a class="dropdown-item" href="#">Account settings</a>
                  <a class="dropdown-item" href="process.php">Log out &raquo;</a>
                </div>
            </li>
        </ul>
    </div>
</div>
</nav>

<script src="https://code.jquery.com/jquery-3.4.1.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.14.7/umd/popper.min.js" integrity="sha384-UO2eT0CpHqdSJQ6hJty5KVphtPhzWj9WO1clHTMGa3JDZwrnQq4sF86dIHNDz0W1" crossorigin="anonymous"></script>
<script src="https://stackpath.bootstrapcdn.com/bootstrap/4.3.1/js/bootstrap.min.js" integrity="sha384-JjSmVgyd0p3pXB1rRibZUAYoIIy6OrQ6VrjIEaFf/nJGzIxFDsf4x0xIM+B07jRM" crossorigin="anonymous"></script>

</body>
</html>

控制台调试怎么说？你讨厌回答？

<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8" />
    <link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0/css/bootstrap.min.css" integrity="sha384-Gn5384xqQ1aoWXA+058RXPxPg6fy4IWvTNh0E263XmFcJlSAwiGgFAW/dAiS6JXm" crossorigin="anonymous">
</head>
<body>
    <nav class="navbar navbar-expand-lg navbar-light bg-white" style="border-bottom: 2px solid #ccc;">
    <div class="container">
        <a class="navbar-brand" href="#">
            <img src="assets/img/logo.png" alt="CraftZealous"/>
        </a>
        <button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#navbarSupportedContent" aria-controls="navbarSupportedContent" aria-expanded="false" aria-label="Toggle navigation">
            <span class="navbar-toggler-icon"></span>
        </button>

    <div class="collapse navbar-collapse" id="navbarSupportedContent">
        <ul class="navbar-nav mr-auto">
            <li class="nav-item">
                <a class="nav-link text-info" href="#" style="font-weight: 700;">HOME</a>
            </li>
            <li class="nav-item">
                <a class="nav-link text-dark" href="#faq">HELP &amp; FAQ</a>    
            </li>
            <li class="nav-item">
                <a class="nav-link text-dark" href="#community">COMMUNITY</a>
            </li>
            <li class="nav-item">
                <a class="nav-link text-dark" href="#">NEWS</a>
            </li>
        </ul>
        <ul class="nav navbar-nav ml-auto">
            <li class="nav-item dropdown">
                <a href="#" class="nav-link dropdown-toggle text-danger" id="dropdown01" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false" style="text-transform:uppercase;">SC</a>
                <div class="dropdown-menu" aria-labelledby="dropdown01">
                  <a class="dropdown-item" href="#">Profile</a>
                  <a class="dropdown-item" href="#">Account settings</a>
                  <a class="dropdown-item" href="process.php">Log out &raquo;</a>
                </div>
            </li>
        </ul>
    </div>
</div>
</nav>

<script src="https://code.jquery.com/jquery-3.4.1.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.14.7/umd/popper.min.js" integrity="sha384-UO2eT0CpHqdSJQ6hJty5KVphtPhzWj9WO1clHTMGa3JDZwrnQq4sF86dIHNDz0W1" crossorigin="anonymous"></script>
<script src="https://stackpath.bootstrapcdn.com/bootstrap/4.3.1/js/bootstrap.min.js" integrity="sha384-JjSmVgyd0p3pXB1rRibZUAYoIIy6OrQ6VrjIEaFf/nJGzIxFDsf4x0xIM+B07jRM" crossorigin="anonymous"></script>

</body>
</html>