And to expand on this further, I think the real driver of the "javascript always changes" is React. Depending on when your React project was built, it can be incompatible in so many different ways with a React project from a different vintage. Sure, a lot of other frameworks and tools that pop up here and there, but none of them are ever widely adopted. When compared to Vue and Angular which I think we can all agree are the other two frameworks of note, React has been very unstable, Vue and Angular appear quite stable.
The javascript language itself hasn't really had a breaking change of note that I can remember in the last 15 years? It's just expanded its API from years and years of browser implementations trying stuff and trying to get to an actual standard. HTML5/ES6/CSS3 brought a new kind of baseline sanity to the whole thing. That's not to say it's a perfect language without quirks, but to say it keeps changing is just not even accurate at all.
python has version evolution, C++ has version evolution, they kinda all do...
Have you worked with Angular much? I've built extensive component libraries (internal) for my org and maintaining the Angular one has been a nightmare. The frequency of breaking changes and conventions has been awful, particularly in the last few years. React, by contrast, has been a breeze ever since they introduced Context and Hooks.
On the app development side, we dealt with 3 major overhauls of PrimeNG's style system before we decided to invest in a custom library just to eliminate the risk of future upgrades. It took us 6 months to migrate our Angular 9 app to 18 because of the PrimeNG dependency. Granted, it's a massive application and they didn't maintain it properly, but I'd hardly call Angular stable regardless.
And then you have the Vue composition API, which was a major shift from Vue 2.
This isn't to say that React has been perfect. Depending on your stack, there are certainly a fair degree of breaking changes (looking at you, Next.js and react router). But that is far from abnormal in the JS world.
Then again, React projects tend to use fast-moving things on top of React, like Redux or NextJS or CRA or whatever. Personally, I enjoy writing stuff in bare React since I like its model, but people tend to steer well clear of that, especially these days with compilers and bundlers and whatnot attached to the frameworks.
> A React class component from 10 years ago will still work in React today perfectly well,
This isn't true.
ComponentWillMount and related methods were deprecated and then removed.
Yes, they allowed an escape hatch of UNSAFE_ComponentWillMount etc, but that still requires work to make it compatible, so it definitely doesn't "[work] perfectly well".
The javascript language itself hasn't really had a breaking change of note that I can remember in the last 15 years? It's just expanded its API from years and years of browser implementations trying stuff and trying to get to an actual standard. HTML5/ES6/CSS3 brought a new kind of baseline sanity to the whole thing. That's not to say it's a perfect language without quirks, but to say it keeps changing is just not even accurate at all.
python has version evolution, C++ has version evolution, they kinda all do...