All modern FE frameworks are effectively observer patterns, it's that there are two camps on how those changes in the state are propagated.

In signals-based platforms (Vue, Svelte, Solid), the signal targets specific subscribers and callbacks where the developer has opted in to state changes.

In React, though `useEffect` looks a lot like Vue's `watch`, they behave entirely differently because the entire component is registered as the callback.

The code examples in my second link [1] above are worth a glance because it makes it very obvious how similar these libraries are when glancing at the code, but how different they are in terms of how they deliver update signals.