Most Asked Node.js Topics
High-frequency Node.js interview topics from software-house rounds — async patterns, the event loop, Express, and a few core internals to explain out loud.
18 topics
- 1
Callback vs Promise vs Async/Await
AsyncJavaScriptMediumThe evolution of handling asynchronous operations in JavaScript/Node.js — from nested callback functions, to Promises, to the cleaner async/await syntax.
Asked in 7 companies
+2 - 2
Event LoopVideo
InternalsEvent LoopHardThe mechanism that allows Node.js to perform non-blocking I/O operations despite being single-threaded, by offloading operations and processing callbacks once the call stack is empty.
Asked in 5 companies+1 - 3
Child processes / clusteringVideo
InternalsScaleHardHow Node.js can spawn additional processes (child_process module) or use the cluster module to take advantage of multi-core systems, since Node runs on a single thread by default.
Asked in 5 companies+2 - 4
MongoDB with Node (Mongoose)
MongoDBMongooseMediumUsing MongoDB (a NoSQL database) with Node.js, often through Mongoose, an Object Data Modeling (ODM) library that provides schema-based solutions.
Asked in 5 companies+1 - 5
Express.js basics
ExpressHTTPEasyExpress is the most common web framework for Node.js, used to build APIs and handle routing, requests, and responses.
Asked in 4 companies - 6
REST API design
HTTPAPIMediumPrinciples of designing RESTful APIs — using HTTP methods (GET, POST, PUT, DELETE) meaningfully to perform operations on resources.
Asked in 4 companies - 7
Node.js architecture / single-threaded nature
InternalsMediumUnderstanding that Node.js runs JavaScript on a single thread but achieves concurrency through non-blocking, asynchronous I/O operations.
Asked in 3 companies+1 - 8
Error handling in Node/Express
ExpressErrorsMediumTechniques for catching and handling errors in asynchronous Node.js code and Express applications, including try/catch blocks and error-handling middleware.
Asked in 2 companies - 9
Middleware (Express)
ExpressEasyFunctions that have access to the request and response objects in an Express app, and can execute code, modify the request/response, or end the request-response cycle.
Asked in 2 companies - 10
JWT / Authentication
AuthJWTMediumUsing JSON Web Tokens to authenticate and authorize users in an API, typically by issuing a signed token after login that's sent with subsequent requests.
Asked in 2 companies - 11
What is Node.js (general)
BasicsEasyA general definition and explanation of what Node.js is — a JavaScript runtime built on Chrome's V8 engine that allows JavaScript to run outside the browser.
Asked in 2 companies - 12
Streams (Node.js)
StreamsPerformanceMediumAn abstraction for working with streaming data in Node.js, allowing data to be read or written piece by piece instead of loading it all into memory at once.
Asked in 1 companies - 13
Microtask queue vs call stackVideo
InternalsEvent LoopHardUnderstanding how the JavaScript engine processes the call stack, the microtask queue (Promises), and the macrotask queue (setTimeout etc.) in a specific order.
Asked in 1 companies - 14
Browser vs Node.jsVideo
BasicsInternalsMediumWhat is the same (JavaScript + V8) and what is different: no DOM/window in Node, Node has fs/http/process, browsers have Web APIs. A very common opening comparison question.
- 15
libuv / thread poolVideo
InternalsPerformanceHardlibuv gives Node its event loop and a small thread pool for some blocking work (file I/O, dns.lookup, crypto). Network I/O is not “multithreaded JS” — the main thread stays free while the OS/libuv wait on sockets.
- 16
CommonJS vs ES Modules
ModulesEasyrequire/module.exports (CommonJS) vs import/export (ESM). Interviewers often ask how you enable ESM in Node and whether modules are cached.
- 17
Worker threads vs clusterVideo
InternalsScaleHardCluster forks extra Node processes to use multiple CPU cores for I/O-bound servers. Worker threads run CPU-heavy JavaScript off the main event loop inside one process. Know which one to pick.
- 18
process.nextTick vs setImmediate vs setTimeout
InternalsEvent LoopHardClassic follow-up after the event loop: nextTick runs before Promises, setTimeout is timers, setImmediate is the check phase. Recursive nextTick can starve I/O.