Installing the Waypoints plugin I’m using Drupal 8.5.4 and I have installed the Advanced CSS/JS Aggregation module. I’m trying to install the Waypoints plugin without success via the module: jQuery waypoints (still on alpha1 for D8). Is there a way to simply install the plugin manually?
Yupp, simply download the Waypoints library, extract and rename the folder to just waypoints, then put it into themes/custom/MYTHEME/libs or into modules/custom/MYMODULE/libs and follow one of the following instructions:

Adding stylesheets (CSS) and JavaScript (JS) to a Drupal 8 theme

Adding stylesheets (CSS) and JavaScript (JS) to a Drupal 8 module



Basically all you have to do is to create the corresponding MYTHEME/MYMODULE.libraries.yml file

waypoints:
  js:
    libs/waypoints/lib/jquery.waypoints.min.js: {}
  dependencies:
    - core/jquery


and then attach the library to all pages via hook_page_attachments() or hook_page_attachments_alter() inside the MYTHEME.theme or MYMODULE.module file.

&lt;?php

function MYTHEME/MYMODULE_page_attachments_alter(&amp;$attachments) {
  $attachments['#attached']['library'][] = 'MYTHEME-or-MYMODULE/waypoints';
}