I would call those anything but boring and mature. They have had a lot of big changes over the last decade and there's no sign of that slowing down. They've been around for a long time, yes, but today they bear only a superficial resemblance to the standards of 25 years ago. JS in particular has changed radically just in the past 5-10 years alone. Search for "how to do X in JS" and you will find that most of the SO questions/answers you get are outdated to the point of being basically wrong. (At least, that has been my experience learning JS in earnest over the last year.)
True, they are not done and moving. But what you did with them 20 years ago still works today. And what you do with them today, likely still works in 20 years. Exceptions obviously exist, though.
- IE9 which finally allowed you to use modern (at the time) web features (like flexbox) without having to support IE specific hacks.
- ES6 which added a lot of syntax changes to JS to make it much nicer to use (and pretty much killed Coffeescript).
- Popularization of type-checking with Typescript and Flow around 2020 which is almost standard these days.
And of course the frameworks evolved a lot as well, but that was mostly project-specific not so much the platform. Someone doing React doesn't care about Angular2 release.
A lot more than that! Typescript is a passing fad! ;)
The Esc key used to stop animated gifs and cancel AJAX calls, it was like a 'stop the world, lemme get off!' button.
Canvas tag (with desynchronized context), Gamepad API, and Web Audio API made the browser into a full-blown operating environment supportive of game development.
CSS3 - grids, aspect-ratio, media queries, oh my!
Web Workers, ASM.js, and WebAssembly -- what even is web development anymore?!?
Of all of those only CSS3 is actually a big deal for most projects (and only a subset of the new CSS3 features). But yeah the new APIs are great and more power is better. Native video/audio playback/streaming was huge as well, but only for a certain class of applications.
I was just highlighting the stuff that really made a huge difference for everyone. Even if you don't use typescript your deps probably do and your IDE can show type hints.
I use Typescript, but I've found comprehensive JSDoc comments do much of the same thing in the right IDE (JetBrains) without paying any of the build time. So, when I have the choice I just use ES2017 (whichever version that has async/await)
Typescript only ever paid off in-terms of capabilities for me when my dependencies went all-in with the runtime type information - felt a lot like Java development marshalling and unmarshalling JSON to objects. But by then, my build times were turning into molasses.
