My favorite autocomplete library is an ancient version of bootstrap-typeahead.js by Twitter. A single file with less than 400 lines of Javascript. They don't make these anymore :)
I use it everywhere where I need autcompletion. For example on the Music-Map:
I did my first autocomplete search UI with that library.
These days, due to the rest of the project, I've been using Angular and Material's Autocomplete component, which I've found very easy to customise for in-memory indexes or hits to a remote ElasticSearch 'suggester' proxy endpoint.
It seems to be missing the most obvious feature: keyboard navigation. My guess is that accessibility is not well implemented either. Probably why other dropdown implementations are bigger code-size wise.
I use it everywhere where I need autcompletion. For example on the Music-Map:
https://www.music-map.com
I made a fork of the code which is available here:
https://www.gibney.org/0g-typeahead