This should have been easier, but I must have misunderstood how this works. After upgrading to Bootstrap 4, for some reason my node_modules didn’t contain fontawesome anymore. I don’t know what I did, but I took it as a sign to upgrade to fontawesome 5. This was a little tricky to follow at first as it works differently to fontawesome 4. Install fontawesome, install the libraries you want to use so they can be used in Bootstrap.
$ npm i --save @fortawesome/fontawesome
$ npm i --save @fortawesome/fontawesome-free-solid
$ npm i --save @fortawesome/fontawesome-free-regular
$ npm i --save @fortawesome/fontawesome-free-brands
In your resources/assets/js/bootstrap.js:
require('@fortawesome/fontawesome');
require('@fortawesome/fontawesome-free-solid');
require('@fortawesome/fontawesome-free-regular');
require(‘@fortawesome/fontawesome-free-brands’);
Compile it using dev or watch.
$ npm run dev
That’s it. Now you can use the class="fa fa-..." tags as expected. You might find some of your existing fa’s are no longer included free. So checkout the fontawesome site and choose icons to replace them with.