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Lesson 7 — useEffect Cheat Sheet

React
In one line: The dependency array controls when useEffect re-runs; return a cleanup function for timers and subscriptions.

Dependency Patterns

1[ ] empty. Runs once, on mount.
2No array. Runs after every render.
3[dep]. Runs when dep changes.
4Cleanup. return () => {...} runs before next effect/unmount.

Fetch on Mount

useEffect(() => { fetch("/api/courses") .then(r => r.json()) .then(setCourses); }, []);