[Suggestion]: lazy initialization example can encourage unsafe patterns - show example

[gmoniava]

Summary

Show example when lazy initialization example can be unsafe.

Page

https://react.dev/reference/rules/components-and-hooks-must-be-pure#lazy-initialization

Details

The lazy initialization section currently presents this pattern as valid:

function ExpenseForm() {
   SuperCalculator.initializeIfNotReady(); // ✅ Good: if it doesn't affect other components

   // Continue rendering...
}

However, I think this example is easy to generalize into a dangerous pattern:

if (ref.current === null) {
   ref.current = createResource();
}

For resources with a lifecycle - subscriptions, event listeners, timers, connections, etc. - creating the resource during render is unsafe because a render is not guaranteed to result in a committed effect.

For example:

function useLegacyStore() {
   const subscriptionRef = useRef(null);

   if (subscriptionRef.current === null) {
     subscriptionRef.current = store.subscribe(() => {
       // ...
     });
   }

   useEffect(() => {
     return () => {
       subscriptionRef.current?.unsubscribe();
     };
   }, []);
}

This can appear to work when components only render as part of normal mount/unmount flows. However, with concurrent rendering or APIs such as Activity, React may render a component without subsequently mounting the
Effect associated with that render.

The subscription has already been created, while its cleanup is tied to an Effect that may never run.

The documentation should make this distinction explicit, perhaps by adding a warning/example.

Inspired by:
https://hackernoon.com/react-activity-when-a-render-no-longer-guarantees-an-effect

[karthik-awebon]

I agree that the distinction between pure initialization (like SuperCalculator) and creating resources with lifecycles (like subscriptions) during render is crucial. The current example could be misinterpreted. I think adding a warning or a specific example for lifecycle-managed resources would significantly improve clarity in the lazy initialization section.

[Mahendra-2006]

I agree that the distinction between pure initialization (like SuperCalculator) and creating resources with lifecycles (like subscriptions) during render is crucial. The current example could be misinterpreted. I think adding a warning or a specific example for lifecycle-managed resources would significantly improve clarity in the lazy initialization section.

Thanks! The intention was to distinguish local initialization, such as SuperCalculator.initalizeIfNotReady() from lifecycle-managed resources like subscriptions. The problematic example is explicitly marked as something not to do during render, followed by Effect-based approach for setup and cleanup. I'll consider making this distinction more explicit.