Bootstrap导航栏下拉故障

Question

So, I just copied a code snippet for the navbar form from bootswatch and directly imported the required JQuery, bootstrap css and js files as you can see in the snippet below. It is being responsive when the browser is resized but when I click the button to get the dropdown menu of the navbar it glitches and doesn't go down and stay there but toggles back on its own.

No tweaks or changes has been made in the code and it works fine on the bootswatch website but it doesn't here. Can anyone explain why and give a fix?

 <link rel="stylesheet" href="https://bootswatch.com/4/united/bootstrap.min.css"> <script src="https://ajax.googleapis.com/ajax/libs/jquery/3.2.1/jquery.min.js"></script> <script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/js/bootstrap.min.js"></script> <nav class="navbar navbar-expand-lg navbar-dark bg-dark"> <a class="navbar-brand" href="#">Navbar</a> <button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#navbarColor02" aria-controls="navbarColor02" aria-expanded="false" aria-label="Toggle navigation" style=""> <span class="navbar-toggler-icon"></span> </button> <div class="collapse navbar-collapse" id="navbarColor02"> <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="#">Features</a> </li> <li class="nav-item"> <a class="nav-link" href="#">Pricing</a> </li> <li class="nav-item"> <a class="nav-link" href="#">About</a> </li> </ul> <form class="form-inline my-2 my-lg-0"> <input class="form-control mr-sm-2" placeholder="Search" type="text"> <button class="btn btn-secondary my-2 my-sm-0" type="submit">Search</button> </form> </div> </nav> 

Answer 1

The problem is in the very thing you mentioned you changed; the Bootstrap and jQuery files. You're using the jQuery from Bootstrap 3.3.7, and the CSS from Bootstrap 4, which have conflicts. Also note that Bootstrap 4 additionally needs Popper.js .

Changing both Bootstrap files to use Bootstrap 4 (and including Popper) fixes this problem:

 <link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0-beta.2/css/bootstrap.min.css"> <script src="https://ajax.googleapis.com/ajax/libs/jquery/3.2.1/jquery.min.js"></script> <script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.12.6/umd/popper.min.js"></script> <script src="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0-beta.2/js/bootstrap.min.js"></script> <nav class="navbar navbar-expand-lg navbar-dark bg-dark"> <a class="navbar-brand" href="#">Navbar</a> <button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#navbarColor02" aria-controls="navbarColor02" aria-expanded="false" aria-label="Toggle navigation" style=""> <span class="navbar-toggler-icon"></span> </button> <div class="collapse navbar-collapse" id="navbarColor02"> <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="#">Features</a> </li> <li class="nav-item"> <a class="nav-link" href="#">Pricing</a> </li> <li class="nav-item"> <a class="nav-link" href="#">About</a> </li> </ul> <form class="form-inline my-2 my-lg-0"> <input class="form-control mr-sm-2" placeholder="Search" type="text"> <button class="btn btn-secondary my-2 my-sm-0" type="submit">Search</button> </form> </div> </nav> 

Hope this helps! :)

Answer 2

That is because bootswatch is using bootstrap 4.0 beta rather than 3 .and for bootstrap4 you will need popper.js

see the demo below

 <script src="https://ajax.googleapis.com/ajax/libs/jquery/3.2.1/jquery.min.js"></script> <script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.13.0/umd/popper.js"></script> <link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0-beta.2/css/bootstrap.min.css"> <script src="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0-beta.2/js/bootstrap.min.js"></script> <nav class="navbar navbar-expand-lg navbar-dark bg-primary"> <a class="navbar-brand" href="#">Navbar</a> <button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#navbarColor01" aria-controls="navbarColor01" aria-expanded="false" aria-label="Toggle navigation" style=""> <span class="navbar-toggler-icon"></span> </button> <div class="collapse navbar-collapse" id="navbarColor01"> <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="#">Features</a> </li> <li class="nav-item"> <a class="nav-link" href="#">Pricing</a> </li> <li class="nav-item"> <a class="nav-link" href="#">About</a> </li> </ul> <form class="form-inline my-2 my-lg-0"> <input class="form-control mr-sm-2" type="text" placeholder="Search"> <button class="btn btn-secondary my-2 my-sm-0" type="submit">Search</button> </form> </div> </nav> 

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EDIT

While trying to include popper.js keep in mind to use only the umd specific directory, not esm or any other. See this previous issue for details