APIs, data and failure
Backend & Node.js Interview Questions
HTTP, databases, Node.js internals, caching and reliability. Learn the trade-offs behind production backend decisions.
40 questions10 easy22 medium8 hard0/40 learned
01What is Node.js and what makes it different from a browser runtime?Easynodejs · runtime · v802How does the Node.js event loop work?Mediumevent loop · libuv · async03Is Node.js single-threaded? What does that actually mean?Mediumnodejs · concurrency · libuv04When would you use worker threads in Node.js?Hardworker threads · cpu-bound · concurrency05How do streams and backpressure work in Node.js?Hardstreams · backpressure · memory06What are Buffers and when do you use them?Easybuffers · binary data · memory07What is the difference between CommonJS and ES modules in Node?Easymodules · esm · commonjs08What is process.nextTick and how does it differ from setImmediate?Hardnexttick · microtasks · event loop09How do you handle errors in a Node.js backend?Mediumerror handling · async · reliability10What is the difference between the cluster module and worker threads?Hardcluster · worker threads · scaling11What happens between a browser sending a request and receiving a response?Easyhttp · networking · dns12How do you choose between REST and GraphQL?Mediumrest · graphql · api design13Which HTTP status codes should a backend engineer know?Easyhttp · status codes · api design14What is idempotency and how do you implement it in an API?Mediumidempotency · retries · api design15How do you design REST resources and endpoints?Mediumrest · resources · api design16How do you version an API and avoid breaking clients?Mediumversioning · api design · compatibility17How do you paginate a large API collection?Mediumpagination · api design · database18What is the difference between authentication and authorization?Easyauthentication · authorization · security19How does JWT authentication work and what are its risks?Mediumjwt · auth · tokens20How do session-based and token-based authentication compare?Mediumsessions · tokens · auth21How does the OAuth 2.0 authorization code flow with PKCE work?Hardoauth2 · pkce · auth22How should you store passwords securely?Mediumpassword hashing · security · argon223When would you choose SQL versus NoSQL?Easysql · nosql · databases24How do database indexes work and when can they hurt?Mediumindexes · sql · query performance25What does ACID mean and how do you use transactions correctly?Mediumacid · transactions · databases26What are database isolation levels and the anomalies they prevent?Hardisolation · transactions · concurrency27How do SQL joins work and how do you choose the right one?Easysql · joins · queries28What is the N+1 query problem and how do you fix it?Mediumn+1 · orm · query performance29What are the trade-offs of using an ORM?Mediumorm · database · sql30Why is database connection pooling important?Mediumconnection pooling · database · performance31What caching strategies should a backend engineer know?Mediumcaching · redis · performance32What is Redis good for in a backend system?Easyredis · caching · data structures33How do you invalidate a cache without serving stale data?Hardcache invalidation · consistency · caching34How do you design rate limiting for an API?Mediumrate limiting · api · redis35Why use a message queue and what are the delivery guarantees?Mediummessage queues · async · distributed systems36How do you build an idempotent message consumer?Hardidempotency · message queues · distributed systems37How do retries and backoff work without making an outage worse?Mediumretries · backoff · reliability38What is a circuit breaker and when should you use one?Mediumcircuit breaker · resilience · distributed systems39What is the difference between horizontal and vertical scaling?Easyscaling · distributed systems · architecture40How do you implement graceful shutdown in a Node.js service?Mediumgraceful shutdown · reliability · deployment
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