It will take a few months just to bring yourself up to speed on mouse/keyboard event bindings and how they interact in one specific browser and one operating system let alone all browsers and operating systems and mobile and that's without even thinking about rendering, templating, network operation wrappers, local storage, camera and sound APIs. The list goes on.

I've been doing this since literally IE 5.5 and I'm still learning new stuff all the time. The fact that you think you can learn all this in a few months is hilarious.

I already learnt most of what I need in one week. I was being pessimistic with 3 months.

If I need to know a particular event, I look it up in the documentation. The stuff you cite is just APIs, I can look that up too. I've used APIs before, you know. Right now I am piping data from Swift to Apple Metal and back, and write GPU code to estimate measurements from the FaceID camera in realtime.

Real programmers are coming to the Web, babe.

Furthermore, from what I see, a lot has changed in JS land. You can basically assume ES2018, with a few exceptions in the library, module systems are part of the standard now, and package managers seem to catch up with that. A lot of what you learnt what is older than 5 years about JS and accompanying APIs, you can basically forget now. Arguably, it might even be better if you had never learnt it in the first place. Because, let's face it, what was going on then was a hot mess of steaming shit.