The other half to this story is many web developers think the browser will magically clean up for them. I've lost track of how many sites I leave open in the background only to come back and find they're using > 1 GB RAM. I can always tell when it happens though because my laptop fan kicks on seemingly randomly.

With a bit of profiling it's usually that these sites just constantly append to the DOM. Without using circular buffers or otherwise cleaning up, eventually the CPU gets pegged doing constant GC. JS and Web development don't obviate the need for fundamentals and good programming practices.