Node is far from the most popular. Majority of websites run on PHP.

Good point, I had forgotten node uses v8. It's powering servers that run node, sure. Not every website uses node. Lemmy I think is rust backend and kbin uses PHP.

But I mean browser specific rendering. They all follow ECMAScript standard but there are things outside of it. In the past __proto__, a way to get an object's prototype, only worked in Spidermonkey. Or how the ECMAScript doesn't specific what order the elements in a for...in loop shows up. Today these are little minor things

They aren't particularly important right now (besides hunting weird bugs) because Google follows the standards more or less. But give Google 100% control and you will start seeing dark patterns slip into the javascript itself