How to import popper.js?

I ran into the same problem.

I downloaded the 'popper.min.js' file from the CDN on the bootstrap website.

See here: https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.11.0/umd/popper.min.js

Easier than compiling the project.

Important: You must include popper after jquery but BEFORE bootstrap.

The official way to install Popper.js is trough npm, Yarn or NuGet.

Use either one of the following commands :

npm i popper.js
yarn add popper.js
PM> Install-Package popper.js

Everything is described in the library readme.

Regarding the "downloads the zip", the zip clearly states that it contains the source code of the library.

Edit:

Starting from version 1.12.0, Popper.js is available as Bower dependency.

This installation method is going to be supported only for the 1.x version of Popper.js and will be removed in 2.x.

You should migrate your dependencies management to a modern system like npm or Yarn, as Bower suggests as well.