React for engineers who have to reason about it under pressure — reconciliation and keys, the useEffect mental model, when memoization actually pays, stale closures, context re-renders, and the Server vs Client Component boundary. The mechanisms behind the interview questions.
6 articles · updated regularly
React Server Components run on the server and ship zero JS; the "use client" directive marks a one-directional boundary that dictates where state, data fetching, and serialization live.
React Context broadcasts to every consumer whenever the provider value's identity changes, so a fresh object each render quietly triggers a re-render storm.
Every React render captures its own props, state, and handlers in a closure — and that snapshot is exactly why your setInterval, event listener, or effect reads "old" values.
A senior engineer's guide to React's three memoization primitives, the referential-equality model underneath them, and why useCallback rarely makes your app faster.
Effects synchronize your component with an external system; most of what you reach for them isn't a synchronization problem at all.
Keys identify siblings across renders; using the array index as a key silently attaches state and DOM to the wrong row on insert, reorder, or delete.