Webpages are dumptrucks for every bad feature anyone ever thought up and are in a constant state of trying to re-framework their way out of the complete mess of utils that get shipped by default. Need a gadget that implements eye tracking via sidechannels? Yeah, they got that. And then justify that with "analytics" or anti-fraud and abuse, and no "click jacking" or whatever crap, and roll it times 1000.

>What on the YouTube home page could possibly require 12MB of JS alone?

all of the code that hoovers up your analytics on what's been looked at, what's been scrolled past, etc. maybe I'm just jaded, but I'd suspect so much of it is nothing but tracking and does little for making the site function

Fun fact: Googles own web performance team recommends avoiding YouTube embeds because they're so obscenely bloated. Placing their <iframe> on a page will pull in about 4MB of assets, most of which is Javascript, even if the user never plays the video.

https://developer.chrome.com/docs/lighthouse/performance/thi...

YouTubes frontend people just don't care about bloat, even when other Googlers are yelling at them to cut it out.

> Assuming 60 characters per line, that’s 200k lines of code?

The code is minified so there's relatively few characters for each source line, if you run it through a pretty-printer to restore sensible formatting then it turns into well over half a million lines of code.

That's the full YouTube player - you were assuming it just has the code for the homepage, but actually it gets the entire player right at the start.