Generally web ui and web api are completely different techs. Even when you are talking node.js on your backend(which is only 1 out of many languages used), you

Generally web ui and web api are completely different techs. Even when you are talking node.js on your backend(which is only 1 out of many languages used), you still are likely dealing with databases and all kinds of things that aren't relevant in 99% of frontend cases. And when I'm doing backend dev work, which is most of what I do, I never deal with DOM and such. There are HUGE differences.