The step that takes the longest is the “transcode with Handbrake” one. On my fairly slow mobile Ryzen 7, it takes about an an hour and a half.
The thing is, you can tweak settings in Handbrake to be faster at the expense of video quality and/or file size.
What I do is to set up a bunch of files and let Handbrake run overnight. In the morning, everything’s done and I can work on the next batch. It helps that I work from home.
Ripping from disc takes about 20 minutes. Copying is as fast as your network. Updating metadata can be done whenever.
There are a lot of programming languages that compile down to JavaScript. I used to be big into Dart, but lost interest when they became solely focused on Flutter.
I personally like using Haxe as it compiles to actual readable JavaScript (and, for fun, a bunch of other languages).