Why Use an Empty useEffect with a MobX Observable Dependency?

Below is an explanation that should help clarify the situation:

What’s Happening in the Component

1. Observable Extraction:
   The component extracts the observable property "refresh" from the language store:

   JSCopied
   const { languageStore: { refresh } } = useStores();

   Even though the value itself isn’t directly used in the JSX, the component is wrapped with observer(), which means it will automatically re-render when any accessed observables change.

2. Empty useEffect as a "Read":
   The empty useEffect is written like this:

   JSCopied
   useEffect(() => {}, [refresh])

   By listing refresh in the dependency array, the code ensures that the component “reads” it during rendering. This read can be important if nothing else in the render (or hooks) uses the observable. If an observable isn’t accessed during render, MobX’s tracking won’t catch updates to it. In other words, this is a common pattern to force the component to subscribe to changes on a value that doesn’t otherwise affect the UI output.

MobX and React Re-renders

• Observer Mechanics:
  MobX's observer will track any observable values read during rendering. When any of these observables update, MobX will trigger a re-render. So if the observable were used directly in JSX, you wouldn’t need any extra mechanism.

• Force Subscription Without UI Use:
  In this scenario, if the language-related data isn’t directly included in the rendered JSX (for example, if its only role is triggering side effects in other parts of your app), the empty useEffect ensures that the component still “subscribes” to changes by reading the observable. The act of reading refresh in the dependency array is enough for MobX’s tracking to kick in—this is why your colleague mentioned it forces re-rendering for language changes.

Conclusion

• Redundancy Debate:
  Technically, if the code were refactored such that the observable is directly used in the render output (or in another hook that MobX tracks), then the empty useEffect wouldn’t be necessary.

• Purpose of the Pattern:
  The empty effect is deliberately there as a safeguard: it ensures that changes to refresh (such as those triggered by setLanguage()) will cause the component to update, even if the observable isn’t otherwise consumed for rendering. This pattern prevents unexpected stale UI when language changes occur.

In summary, your colleague’s explanation isn’t entirely off—the pattern is there to ensure the component “listens” for language changes, but it stems from MobX’s requirement to read observables during render to track them, rather than React automatically re-rendering by simply listing a dependency in an effect.