Bootstrap 4 navbarDropdown 不起作用？答案

【问题标题】：Bootstrap 4 navbarDropdown is not working?Bootstrap 4 navbarDropdown 不起作用？
【发布时间】：2017-11-22 13:14:12
【问题描述】：

我不知道为什么我在设置导航栏下拉菜单时遇到很多问题。它说 popper 没有定义和意外的令牌支持。下面的代码只是文档中的示例。请帮帮我，这真的很令人沮丧。

<!DOCTYPE html>
<html>
    <head>
        <link rel="stylesheet" type="text/css"  href="style.css" />
        <link href="https://fonts.googleapis.com/css?family=Source+Sans+Pro" rel="stylesheet">
        <link href="bootstrap/css/bootstrap.min.css" rel="stylesheet">
        <script type="text/javascript" src="jquery.min.js"></script>
        <script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.12.6/popper.min.js"></script>
        <script type="text/javascript" src="bootstrap/js/bootstrap.min.js"></script>

    </head>
    <body>

        <nav class="navbar navbar-expand-lg navbar-light bg-light">
            <a class="navbar-brand" href="#">Navbar</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 active">
                        <a class="nav-link" href="#">Home <span class="sr-only">(current)</span></a>
                    </li>
                    <li class="nav-item">
                        <a class="nav-link" href="#">Link</a>
                    </li>
                    <li class="nav-item dropdown">
                        <a class="nav-link dropdown-toggle" href="#" id="navbarDropdown" role="button" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">
                            Dropdown
                        </a>
                        <div class="dropdown-menu" aria-labelledby="navbarDropdown">
                            <a class="dropdown-item" href="#">Action</a>
                            <a class="dropdown-item" href="#">Another action</a>
                            <div class="dropdown-divider"></div>
                            <a class="dropdown-item" href="#">Something else here</a>
                        </div>
                    </li>
                    <li class="nav-item">
                        <a class="nav-link disabled" href="#">Disabled</a>
                    </li>
                </ul>
                <form class="form-inline my-2 my-lg-0">
                    <input class="form-control mr-sm-2" type="search" placeholder="Search" aria-label="Search">
                    <button class="btn btn-outline-success my-2 my-sm-0" type="submit">Search</button>
                </form>
            </div>
        </nav>
      </body>

</html>

【问题讨论】：

标签： html twitter-bootstrap popper.js

【解决方案1】：

您使用的是什么引导版本您可以尝试在此网络的头部添加此代码并替换您在头部使用的引导程序吗？

<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0-beta.2/css/bootstrap.min.css" integrity="sha384-PsH8R72JQ3SOdhVi3uxftmaW6Vc51MKb0q5P2rRUpPvrszuE4W1povHYgTpBfshb" crossorigin="anonymous">

<script src="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0-beta.2/js/bootstrap.min.js" integrity="sha384-alpBpkh1PFOepccYVYDB4do5UnbKysX5WZXm3XxPqe5iKTfUKjNkCk9SaVuEZflJ" crossorigin="anonymous"></script>

Bootstrap 下拉菜单需要 Popper.js

https://www.codeply.com/go/ENrIDOUDtc

【讨论】：