I’d agree that if you’re looking to have a career in front-end your order should be some JavaScript, then React/Angular and possibly Typescript, but after that I’d still recommend you go back and really learn JavaScript. It doesn’t often happen but sometimes you run into a situation where that knowledge does come in handy. You can introduce bugs in your React code if you don’t understand closures for example, to use a library like redux-saga you need to understand generator functions, you may run into code where you need to know how the “this” keyword works, etc. A more junior dev needing help with those is fine, but I’d expect a senior dev to be able to navigate those type of situations on their own most of the time.

Solving bugs is important but more to your point a good senior dev knowing those things provides flexibility and empowerment. Sometimes there is a more direct solution than what the internally available tools provide.

There's an effect where young people watch Seinfeld and find it unfunny and derivative. That's not because it's true, but because they watched stuff that had copied what Seinfeld did first.

People look at Crockford's "JS: The Good Parts" and comment on how it's obvious. It wasn't obvious then and that's why the book was so well received. Languages have radically copied the good parts JS since then while JS has lost most of the worst parts which means that when you move to JS, it's a much less radical shift.

First-class functions and closures with all their implications (IIFE, module pattern, callback/continuation, lambdas, .map() and it's ilk, currying, etc) have all caught on as a result.

Immutable data or more precisely, treating data as immutable and letting the GC sort it out was a huge boon for UI development.

Promises/futures seem ubiquitous these days, but that's strictly because of JS libraries introducing them in 2005 (twisted library introduced them in Python in 2001, but Python wasn't super popular then and twisted has never been popular at all).

I'd also say that the push for pattern matching has also been fueled by ES6.

In truth, StandardML (SML) and Scheme had been doing most of this (and much more) since the 70s, but for whatever reason, they have been rejected by mainstream developers. Hopefully, one day we will recognize this and switch development away from languages with these features tacked on to ones where they are baked in and cohesive.

what you're saying is the equivalent of you'll learn django orm or whatever orm instead of SQL. Yeah in the short term, you've immediate productivity gains. But in the long term, you lose out as the ORM | Framework API's churn - while the base language itself remains stable.

Invest in the basics, and you'll never lose. SQL, HTML, JS. No need to keep learning or relearning frameworks or libraries.