> Examine html source of such sites as
Just because someone uses a technology, doesn't mean it's good. I could point to plenty of sites still using first versions of Angular. Is it workable? Yes. Is it good?
Also, I'd skip youtube as an example. No idea what incentives they had internally to re-write everything in web components, but they (and the web) paid dearly for it:
- Youtube was re-written in v0 of Custom Components. Which was deprecated as soon as they re-wrote it. Chrome couldn't remove v0 from the browser until Youtube was re-written (undoubtedly at great expense) with v1 four years later
- The polyfill for v0 was famously extremely slow in Firefox. Given that Youtube is one of the most popular websites (if not the most popular), you can imagine what it did to Firefox's image.
If you have an extra billion of dollars for such shenanigans, sure, knock yourself out (especially if it helps to cripple your competition).
Also IIRC GitHub is using React as well now, but I can't find the relevant link and discussion right now.