react-frontend

React Frontend

Verify before implementing: For App Router patterns, React 19 APIs, or version-specific behavior, look up current docs (Context7 query-docs if available, else the framework's official docs via web search) before writing code. Training data may lag current releases.

Working rules

• Keep derived state in render and user actions in event handlers; use effects for external synchronization.
• Give async work a lifecycle and cancellation policy; represent failure separately from pending and empty data.
• Bind cache keys to the request's identity. A tenant-scoped key can receive another tenant's response when server session state changes first. Keep request scope and cache identity consistent throughout context switches. Verify isolation with mounted consumers, in-flight requests, and failed refetches.
• Preserve focus when hiding interactive regions and exercise keyboard navigation in a real browser.
• Validate and authorize every public server action; send only needed fields across server/client boundaries.
• Measure performance changes and test user-visible behavior, not type-checking alone.

Effects Decision Tree

Effects are escape hatches; most logic should NOT use effects.

Effect rules:

• Never suppress the linter; fix the code instead
• Use updater functions (setItems(prev => [...prev, item])) to remove state dependencies
• Move objects/functions inside effects to stabilize dependencies
• useEffectEvent for non-reactive values (e.g., theme in a connection effect)
• Always return cleanup for subscriptions, connections, listeners
• Data fetching cancellation (pick by situation): AbortController for fetch; ignore flag for non-cancellable promises. With React Query, pass the query function's signal to the transport, such as queryFn: ({ signal }) => fetch(url, { signal }). Without consuming that signal, an unused query can finish and populate the cache; do not describe that behavior as transport cancellation.
• A settled request is not completed initialization. Consume a one-time initialization latch only after applying usable data or observing a successful terminal empty result. Test empty-then-populated responses within one mount. Verify that later refetches preserve user edits.