When I say 'compiled' I'm abusing the term to mean they have any kind of build step, and could not be written the same way by
dropping code into a script tag [1] as said in the parent comment. For the most part what comes out of the build process could be replaced with WASM at a whim, whenever it gains access to all the DOM and browser APIs.
The majority of news, social media, video, media sites, message boards, online games and web apps fit this description. I'd wager that 95%+ of websites produced by a paid professional today are in this category. Unfortunately no, I don't have data to back this up, only my perception as a web developer.
[1] due to relying on a module system, es6 transpiler, etc