Full Stack developer interview questions

Apply a limiter early, especially on login and signup, to slow brute force and abuse.

An index is a data structure that lets MongoDB find documents without scanning the whole collection.

Aggregation is a sequence of stages such as match, group, lookup, and project that transform documents on the server.

populate replaces stored ObjectId references with the related documents in a follow-up query.

Embed data that is read together and stays bounded, such as an address on a user.

lean() returns plain JavaScript objects instead of full Mongoose documents.

Offset pagination uses skip and limit, which is simple but slow on large skips.

Only call hooks at the top level of a React function, never inside loops or conditions.

useMemo caches an expensive calculation between renders.

Context passes data through the tree without prop drilling, such as theme or the current user.

A controlled input takes its value from React state and updates through onChange.

React.memo skips re-rendering a component when its props are shallowly equal.

Trigger the request in useEffect or a data library such as React Query, handle loading and error states, and cancel or ignore stale responses.

Lift state when two nearby components share data.

A custom hook is a function starting with use that calls other hooks.

An access token is short-lived and sent on each API call.

SameSite=Lax or Strict stops the browser from sending cookies on most cross-site requests, which blocks classic CSRF.

A salt is random data mixed into the hash so two users with the same password get different hashes.

A middleware reads the cookie or Authorization header, verifies the JWT or session, and attaches req.user.

OAuth lets the user sign in with a provider such as Google without sharing their password with you.