react-useeffect

React useEffect best practices guide covering when to use Effects and superior alternatives. Effects are an escape hatch from React. They let you synchronize with external systems. If there is no external system involved, you shouldn't need an Effect. - Teaches the escape-hatch nature of Effects: use only for synchronizing with external systems, not for derived state, expensive calculations, or user event responses - Provides a decision tree and quick-reference table mapping common situations (data fetching, state derivation, prop changes) to the correct React pattern - Covers when NOT to use Effects: transforming data for render, handling user events, deriving state, and chaining state updates - Recommends alternatives including direct calculation during render, useMemo for expensive computations, key prop for state reset, and useSyncExternalStore for subscriptions - Synchronizing with external systems (non-React widgets, browser APIs) - Subscriptions to external stores (use useSyncExternalStore when possible) - Analytics/logging that runs because component displayed - Data fetching with proper cleanup (or use framework's built-in mechanism) - Transforming data for rendering - Calculate at top level, re-runs automatically - Handling user events - Use event handlers, you know exactly what happened - Deriving state - Just compute it: const fullName = firstName + ' ' + lastName...