A while ago (8 years in fact) I wanted to make something like this. I made a slightly half-assed React library that used twgl to overlay a shader on an element on a page (or a canvas for some effects). One thing I had was measuring where an element was on the page and then using absolute positioning to put a canvas over it so effects could expand beyond the confines of the element. I still think that has potential for some fun things but browsers aren't really fast enough to keep it in the right place with scrolling so it never works properly. https://react-neon.ooer.com/ + https://github.com/onion2k/react-neon

These new libraries are much better than anything I came up with.