I think the main pain point is towards front end appearance/interactions. Js as a language has gotten more ergonomic, but it's been Turing complete forever. As a practical matter, the pain comes when you say "I want to align x" and come to learn that every browser has different flags to accomplish the task. I'm sure you've seen the fat stacks of moz/ie/opera checks and flags before. I know that example is bad, but I can't think of a good one at the moment, I rarely touch front end.