Full Stack Developer
Interview Questions.
16 practice questions across 12 skills — each with what the interviewer is really listening for. Prepare with intent, not guesswork.
Free · No signup · Grouped by skill
How to use this page
Don't memorise answers. For each question, read what the interviewer is looking for, then practise answering out loud in your own words with a real example. The notes describe strong answers and common red flags — they are for your prep, not a script.
REST APIs
2 questionsWalk me through what happens end-to-end when a user submits a form on a full-stack app you built.
IntermediateWhat the interviewer is looking for: Strong answers trace the request from client validation, through the HTTP call, server validation, database write, and response back to the UI state. Skipping validation or error handling on either side is a red flag.
How do you design an API endpoint so the frontend can show clear loading, success, and error states?
IntermediateWhat the interviewer is looking for: Look for meaningful status codes, consistent error shapes, and predictable responses the UI can branch on. Returning 200 with an error body, or vague errors, are red flags.
Node.js
2 questionsHow do you decide what logic belongs on the frontend versus the backend?
IntermediateWhat the interviewer is looking for: Look for keeping trust-sensitive validation and business rules server-side while using the client for UX, and never trusting client input. Putting authorization checks only on the frontend is a serious red flag.
Explain the event loop in Node.js and why blocking it is dangerous.
AdvancedWhat the interviewer is looking for: A strong answer covers the single-threaded event loop, non-blocking I/O, and that CPU-heavy synchronous work stalls all requests. Believing Node handles each request on its own thread is a red flag.
React
1 questionHow do you manage state that needs to stay in sync between React components?
IntermediateWhat the interviewer is looking for: Look for lifting state up, context for cross-cutting state, and reaching for a store only when justified. Prop-drilling everything or global state for everything are both red flags.
JavaScript
1 questionWhat is the difference between == and === in JavaScript, and why default to strict equality?
BasicWhat the interviewer is looking for: The candidate should explain type coercion and give a surprising example, recommending === by default. Not knowing coercion happens is a red flag.
HTML
1 questionWhy does semantic HTML and a sensible CSS layout still matter when you are mostly writing React?
BasicWhat the interviewer is looking for: Look for accessibility, SEO, and maintainability, not just visual output. Treating markup and CSS as an afterthought behind a framework is a red flag.
SQL
1 questionYou need to join data across two tables to render a dashboard. How do you write and check the SQL?
IntermediateWhat the interviewer is looking for: Strong answers choose the correct join, guard against row multiplication, and consider indexes for performance. Fetching everything and joining in application code by default is a red flag.
Git
1 questionYour feature branch conflicts with main after a long-running task. How do you integrate safely with Git?
IntermediateWhat the interviewer is looking for: A strong answer describes merging or rebasing main in, resolving conflicts deliberately, and testing before pushing. Force-pushing over shared history or blindly accepting one side are red flags.
TypeScript
1 questionWhat does TypeScript buy you on a full-stack project, and where does it not help?
IntermediateWhat the interviewer is looking for: Look for compile-time safety and shared types across client and server, with the caveat that it does not validate runtime data from the network. Assuming types guarantee runtime correctness is a red flag.
JWT
1 questionHow would you implement authentication with JWTs, and what are the common pitfalls?
AdvancedWhat the interviewer is looking for: Strong candidates cover signing, expiry, secure storage, and refresh, and warn about XSS with localStorage and the inability to revoke stateless tokens easily. Storing secrets client-side or ignoring expiry are red flags.
Docker
1 questionHow do you decide when to reach for Docker in your development workflow?
IntermediateWhat the interviewer is looking for: Look for reproducible environments and parity between dev and prod, plus awareness of image size and layering. Not being able to explain why containers help beyond 'it works on my machine' is a red flag.
Problem-Solving
2 questionsYou are asked to add a feature that touches the database, the API, and the UI. How do you sequence the work?
IntermediateWhat the interviewer is looking for: Strong answers design the data model and contract first, then build vertically with testing at each layer. Starting with UI polish before the contract is stable is a red flag.
How do you handle a bug that only reproduces in production and not locally?
AdvancedWhat the interviewer is looking for: Look for reproducing with prod-like data, checking logs and environment differences, and adding observability rather than guessing. Random changes deployed to prod to 'see if it fixes it' are a red flag.
Collaboration
1 questionHow do you keep frontend and backend teammates aligned when you own both sides of a feature?
BasicWhat the interviewer is looking for: Look for agreeing on the API contract early, clear communication, and documenting decisions. Building both sides in isolation and integrating at the end is a red flag.
Behavioural & role-general
1 questionTell me about a full-stack feature you owned end to end. What was hard and how did you handle it?
BasicWhat the interviewer is looking for: Strong answers show ownership across layers, real trade-offs, and lessons learned. Vague 'we built it' stories with no personal decisions are red flags.