State was never easy. GUI apps have struggled with this as well. Hence you have the proliferation of different approaches: MVC, MVVM, various attempts at streams and observables, state machines, flows... All of these came from outside the web world. And, as most things in the web, all these concepts either arrived too late, or couldn't be implemented properly for various reasons.

And the problem is exacerbated by the fact that people are trying to push native app paradigms onto what is still a document-rendering system. So where you can have thousands of objects rendered at 120Hz on a mobile phone, the web struggles showing and animating a few hundred nodes even on a desktop computer. So you have to think of all the machinery to change as few DOM nodes as possible.

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As for the difficulty...

The difficulty usually comes from people mixing up two concepts: the state of data, and the state of the UI.

E.g. while a music player should present data on the currently playing song (state of data), there's a few other things that are UI-only. E.g.: there's a timer running on when to hide the controls (that has to be reset/disabled when a button is pressed)

>GUI apps have struggled with this as well

And when we made mistakes there, it was usually because we took short cuts instead of respecting clean abstractions.

>So you have to think of all the machinery to change as few DOM nodes as possible.

This is where I get off the train in regards to JS frontend frameworks. We should know the state our data. We should also know the state of our display components, whether they are canvas elements rendering more complex data or mere tables. KISS principles apply here.

"All the machinery" of a framework isn't necessary to handle the synchronization between the two. Especially when it mandates ridiculous build steps, thousands of dependencies, opaque "magic", huge blobs of minified JS and loading spinners.

>The difficulty usually comes from people mixing up two concepts: the state of data, and the state of the UI.

Agreed 100%. Which is why I like the <template> element. It is a dose of sanity allowing explicit separation of code and document. I suspect this is the other poster's objection to HTML inside of JS.