I’ve been coding in JS for years, but would like to dive a bit deeper into the ecosystem around it.
For Cloudflare Workers specifically: first, learn regular Web Workers, then read everything from kentonv who's the tech lead for CF Workers, and a user here. He's written many (disjointed) pieces on Workers both here on HN and on the CF community board. Additionally, Cloudflare Developers Discord (https://discord.com/invite/cloudflaredev) has a very active channel for Workers with people discussing implementation details and edge cases.
Studying the source code for a JS implementation is also a good step. QuickJS is a good one.