Bootstrap 4 Beta - Is Popper.js required?
Popper.js is not required if you use bootstrap.bundle.js or bootstrap.bundle.min.js instead of bootstrap.js or bootstrap.min.js. That's because the bootstrap.bundle.* libraries contain popper internally. You can download all the bootstrap files from here
Alternatively, if you only use the non-Popper JS functionality of bootstrap, you can fake Popper and load bootstrap (thus Bootstrap will work and won't throw an error about Popper being missing):
<script>
window.Popper = {}
</script>
<script src="js/bootstrap.min.js"></script>
Not anymore, check THIS issue It seems Bootstrap has bundled Popper and Bootstrap v4 into a bundle.min.js file that is available if you try downloading now. HERE is a link directly to the bundled min file. Hope that helps someone who is not interested in adding a separate popper file
If you search for "popper" in Bootstrap 4's documentation, the following results will come up:
Tooltips rely on the 3rd party library Popper.js for positioning.
Popovers rely on the 3rd party library Popper.js for positioning.
Dropdowns are built on a third party library, Popper.js, which provides dynamic positioning and viewport detection.
So these are the Bootstrap 4 components that need Popper.js.
Though Popper.js is stated as required for Bootstrap 4, and Bootstrap 4 JS logs an error if it can't find Popper, you can still use Bootstrap 4 JS without Popper, if you don't need tooltips, popovers, dropdowns, nor modals.
For example navbar's JS functionality (mobile menu on the right) works well:
<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0-beta/css/bootstrap.min.css" integrity="sha384-/Y6pD6FV/Vv2HJnA6t+vslU6fwYXjCFtcEpHbNJ0lyAFsXTsjBbfaDjzALeQsN6M" crossorigin="anonymous">
<script src="https://code.jquery.com/jquery-3.2.1.slim.min.js" integrity="sha384-KJ3o2DKtIkvYIK3UENzmM7KCkRr/rE9/Qpg6aAZGJwFDMVNA/GpGFF93hXpG5KkN" crossorigin="anonymous"></script>
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0-beta/js/bootstrap.min.js" integrity="sha384-h0AbiXch4ZDo7tp9hKZ4TsHbi047NrKGLO3SEJAg45jXxnGIfYzk4Si90RDIqNm1" crossorigin="anonymous"></script>
<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">
<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="text" placeholder="Search" aria-label="Search">
<button class="btn btn-outline-success my-2 my-sm-0" type="submit">Search</button>
</form>
</div>
</nav>