Libraries
In my opinion there are really three big players in the world of motion design javascript libraries:
Matt Perry
Creator of Framer Motion, PopMotion and the newer Motion (previously known as Motion One) Matt’s work has been focused on creating React motion libraries however the newest iteration now uses the same engine for a vanilla Javascript version. Strong declaritive API, incredible performance but lacking when it comes to timeline features.
Julian Garnier
Creator of AnimeJS. The library is lightweight, quick to learn and yet very robust. I probably use it 80% of the time for anything more complicated than CSS transitions.
The team at GSAP
Creator of GSAP: GreenSock Animation Platform. This is my go to library for complex animation timelines and very interactive components. GSAP is also now free since Webflow purchased the company.