If it makes you feel any better, that's because there isn't a coherent mental model. If you've ever heard of the ORM/Relational impedance mismatch, it's got nothing on the set of impedance mismatches between the way servers like to work, the HTTP protocol (and its still very page-based orientation in a world of streams), the browser's DOM model, and how Javascript works, especially if you want to get excellent performance out of it.
It is my opinion that this is why you see so much churn in the web world; the continuous iterations on client-side frameworks, server-side frameworks, this Javascript DOM library, that Javascript DOM library, now an integrated framework, now recommending assembling your own from bits and pieces... it's all a reflection of the fact that none of these pieces particularly work all that well together in the way we'd really like them to. There's a ton of possibilities, all of them frankly pretty bad in most ways but good for this one use case, but a different use case for each tech, and that's a recipe for a lot of churn.
My recommendation to anyone getting into this world is A: learn the basics of HTTP B: learn the basics of HTML C: clock some time with Javascript's basic DOM interface and maybe jQuery and then D: relax about the whole thing, unless you really think you're going to build an app that scales up to the tens of thousands of simultaneous users. The truth is that when it comes down to it there are still plenty of applications you can successfully build and deploy using completely 2005 technologies... and the dirty secret truth is that you may well beat someone to market who is over-invested in staying Up To Date and constantly throwing away all their skills.
(You will not beat to market someone who is judiciously staying up to date, and carefully picking and choosing what modern tech to learn and deploy. But you still probably won't be that far behind them, either. And that is not the person who is actually freaking everyone out about the web; it's the guy vigorously selling Vue.js or whatever modern thing as the hot new thing and that all previous JS libraries are now trash that should be used by nobody, when six months ago they were saying the same thing about something else.)
