React useEffect Dependency Warning and Infinite Loops

1. Missing dependencies array causing effect to run on every render
2. Object or function dependency not memoized, causing different reference each render
3. Dependency array doesn't include all used variables (ESLint warning)
4. Infinite loop: effect updates dependency, triggering effect again
5. Using stale closures, accessing old state from effect

Always include dependencies array: useEffect(() => { ... }, [dep1, dep2]) prevents infinite loops.

Memoize dependencies: For objects/functions, use useMemo/useCallback:
const user = useMemo(() => ({id: 1}), []);
useEffect(() => { ... }, [user])

Fix ESLint warnings: If warning says missing dependency, add it. If adding causes loop, memoize it first.

Handle stale state: For state updates in effects, use updater function: setCount(c => c + 1) instead of using count from closure.