Browser Rendering Performance

Doesn't that cause either stuttering, or flickering in the viewport?

HTML renderers often have choppy animation and transitions.

CSS rendering engines will need to get much faster before anything like this wouldn't feel glitchy or pop-in.

I've noticed this too, and my guess is they're doing animations on the CPU.

It's definitely not slow at rendering. Network performance isn't great, but try resizing the window.

I wouldn't say "common". If you avoid "DOM thrashing" (where your code repeatedly mutates the DOM and then measures it and then mutates and then measures), the browser is pretty good at batching these computations and the vast majority of projects will never run into this as a problem. And thrashing is something you should solve by improving your JS, not mitigate with this API.

I'm not going to dive in and play with it, but often it can help to add the CSS rule "transform: translateZ(0)" in order to force rendering to the GPU instead of CPU.

Not as fast for rendering complex apps with lots of content…

Immediate rendering consumes an insane amount of CPU.

The GPU is drawing 60 times a second regardless of whether the page is static. Not sure how they do their streaming to the GPU, but there will be state changes every time you scroll, or click a button, etc., even on a static page.