NodeJS Interview Guide 100+ Questions & Answers

Explore how Node.js executes code through the event loop, detailing the synchronous start, microtask and macro phase processes, and the roles of promises, process.nextTick, setImmediate, and I/O callbacks.

Explain blocking versus non-blocking operations in node.js, noting I/O handling, CPU-bound tasks, and how the event loop uses asynchronous callbacks.

Learn how blocking the event loop harms performance in NodeJS, and how worker threads prevent unresponsiveness by offloading tasks. Identify which synchronous NodeJS APIs—encryption, compression, and file system—can block.

Libuv delegates io and async cpu tasks to the thread pool during the poll phase; tasks are assigned when a worker is free, otherwise queued.

Learn how Node.js cluster mode uses a built-in load balancer to spawn multiple workers on a single port, leveraging CPU cores for faster requests, and how PM2 offers production-grade clustering.

Semantic versioning uses major, minor, and patch numbers to signal changes: major releases bring breaking changes, minor adds features, patches fix bugs, and check changelogs and run tests before deployment.

Learn robust error handling in NodeJS applications by mastering try/catch with promises, finally, and proper rejection handling; implement error handling middleware in Express and NestJS, and emphasize logging and TypeScript.

Explore the four native Node.js streams—writable, readable, duplex, and transform—and see how data is written, read, transformed, and piped in practical examples like uppercase conversion.

High watermark defines a stream’s internal buffer size in bytes; adjust read and write stream values and monitor readable and writable length to manage data flow.

Master streaming data in Node.js by handling range requests, creating a readable stream, and piping it to the response to deliver 206 partial content with range headers.

Explore why the plain pipe API in Node.js lacks automatic error handling and can cause memory leaks; learn how the pipeline API catches errors and safely destroys affected streams.

Explore the main http methods and their top use cases, including get, post, put, patch, delete, head and options, plus connect and trace, with notes on idempotence and request bodies.

Explore which http methods are idempotent or safe, including get, head, options, trace, put, and delete, and why post is not, with patch nuances.

Learn how http status code classes map to client and server responses, with examples of common codes like 200, 201, 204, 206, 301–302, 304, 400–405, 500–503.

Understand how HTTP requests include method, URL, path parameters, query parameters, headers, body, and cookies for session management and identifying resources.

Explore representational state transfer, a language-agnostic, stateless API style using http methods and json, with xml or text options and soap contrasts, with security considerations.

GraphQL is a specification for querying and manipulating data that solves over fetching and under fetching with a single post endpoint, a strict schema, and language-agnostic JSON responses.