React

Components, state, effects, custom hooks, Context, performance and server state.

1. 1Components, props and JSXPure components, JSX rules, keys in lists and composition with children.
2. 2State, derivation and reducersUsing useState correctly, immutable updates, derived state and useReducer.
3. 3Effects and useRefWhen you need useEffect, cleanup, and when you DON'T need it.
4. 4Custom hooksReusable logic, the rules of hooks, useSyncExternalStore.
5. 5Context, portals, error boundariesNo prop drilling, rendering elsewhere in the DOM, errors isolated per section.
6. 6Performance in ReactWhy a component re-renders, memo, useMemo, useCallback, useTransition, virtualization.
7. 7Server state and TanStack QueryWhy server data isn't useState, query keys, staleTime and invalidation.