Node JS Interview Masterclass: Top 200 Questions (PDF)(2026)

Explore the basics of Node.js through essential questions, and revise even familiar topics to uncover deeper pointers about Node.js.

Node.js is a runtime environment that executes JavaScript on the server side, not a language or framework. The runtime handles memory management and translates code to machine language.

Explore how runtime environments provide infrastructure for code execution and memory and I/O services, while frameworks wrap them to simplify development with libraries, reusable classes, and tools.

Node.js runs JavaScript on the server, while Express.js is a Node.js framework that simplifies building web apps and APIs with routing and middleware.

Contrast client-side and server-side JavaScript, showing how browsers render UI and handle UI interactions while Node.js processes data storage, authentication, authorization, and API data fetching.

Explore synchronous programming on a single thread, where tasks execute one after another and blocking reduces performance. Compare this with asynchronous approaches in Node to improve time efficiency.

Explore asynchronous programming in Node.js applications, using a single thread to initiate multiple tasks with non-blocking, event-driven execution.

The lecture compares synchronous and asynchronous programming, presenting point-by-point differences. It highlights the advantages of asynchronous programming over synchronous.

Explore how events originate from event emitters, flow through the event queue, and are processed by the event loop in node's event-driven architecture, with event handlers implementing asynchronous actions.

Relate Node.js features to advantages, including asynchronous operation, V8 engine, event-driven architecture, cross-platform support, and JavaScript usage, to show concurrent handling, speed, and scalability.

Assess the disadvantages of node and decide when to use it for real-time apps, REST APIs, and microservices. Avoid node for CPU-intensive tasks that require multi-threading.

Set up a node.js project quickly by installing node.js, installing a code editor, creating a project folder, running npm init -y, creating app.js, and running node app.js in the terminal.

Explore npm, the node package manager, and how the node_modules folder stores a project's dependencies and libraries, why removing dependencies harms functionality, and why you should never touch this folder.

Explore the role of the package.json file in node projects, and understand how it stores project metadata such as name, version, description, author, and license.

Explore the different ways to export a module in node js, including module.exports and direct exports, and learn how to make functions, variables, and objects accessible outside the file.

Export the module to make its functions accessible outside the module; without exporting, the module functions stay private and unavailable externally.

Learn to import single or multiple functions from a node module using require; use the shortcut module.exports = function for one function, and module.exports.functionName for multiple functions.

Explain how Node.js wraps each module in a function, called the module wrapper function, to simplify execution and keep code shorter for developers.

Explore the five built-in node modules most commonly used in projects, including fs, path, os, events, and http, and learn their roles and importance.

Explore the fs module in node for managing files, using readFile and writeFile, plus appendFile, unlink, readdir, mkdir, and rmdir to read, create, and delete data.

Explore the node path module to join and parse paths, and identify properties such as route name, directory, base name, file extension, and file name.

Learn how the OS module in Node.js enables cross-platform apps by importing it and using functions like type, userInfo, totalMemory, and freeMemory to interact with the operating system.

Learn how the node events module powers event driven architecture with the event emitter, on registration, and emit handling, including how the event loop coordinates listeners and emissions.

Differentiate a function as a reusable piece of code from an event as an action that triggers one or more functions within a node api application.

The http module in node creates an http server that listens on a port, receives requests from the UI, and sends responses back to the client.

Explain how the http.createServer method creates an HTTP server in node.js and sets up a request–response callback. Listen on a port to handle browser requests.

Explore the advantages of using Express with Node.js. Learn how Express simplifies web development, enables middleware handling, offers flexible routing, and supports template engine integration for dynamic server-side HTML.

Install Express in a Node.js project by running npm install express in the terminal, then start using the Express framework and its features in your code.

Learn to create an http server with the http module and express, including importing express, creating an app, setting a port, and listening on localhost:3000, and explore express advantages.

Explore Express middleware in node js, learn what middleware is, how to implement it, and how the next parameter powers the request pipeline.

Understand how middleware acts as a middleman between requests and Express endpoints, forming a request pipeline that logs, authenticates, and secures http requests before reaching get, post, and put endpoints.

Learn the purpose of the next parameter in Express.js and how the next callback passes control to the next middleware in the stack, enabling multiple middleware execution.

Apply middleware globally to a specific route using app.use with a path, so it runs only when the url contains the given string and shows results.

Explore the types of middleware in Express, with practical guidance on when to use each type in different app scenarios, illustrated by examples from logging and authentication.

Learn how error handling middleware works in Node.js, capturing errors with the error parameter, logging the stack trace, and delivering a user friendly message with a proper status code.

Enable serving static files with Express by using the built-in static middleware inside App.use, serving the public folder directly without authentication.

Learn how third-party middlewares extend express apps, install via npm, import, and wire with app.use; explore helmet for security headers, body-parser for parsing requests, and compression to boost performance.

Discover how express middleware enhances modularity and reusability, improves request handling, enables flexible control flow, and supports third party middlewares in building scalable Node.js apps.

Routing in Express directs HTTP requests to the correct controller based on the request method and URL path, using middleware to route to orders, products, or payments as needed.

Clarify how middleware differs from routing in Express: middleware is a function that can access request and response and run actions like authorization, while routing directs requests to handlers.

Define routes in express using app.get, post, put, and delete with route handlers for root and login paths. Start the server and observe route execution.

Define an Express.js app, apply authentication and logging middleware, import and use controllers, define routes based on URL and request method to dispatch to controller functions, then start the server.

Define route handlers by passing a callback function as the second argument to handle get requests, process the request, and generate the response for your later revision.

Explore route parameters in Express. Access route parameters as dynamic values sent with the request url, and retrieve the user id from request.params for use in your app.

Explains how to create an Express router object and define routes with get, post, put, and delete, then export and mount it with app.use for API paths.

Learn the four router methods: get, post, put, and delete, and understand that post uses post requests while get uses get requests.

Compare app.get and router.get: app.get defines routes on the app and auto-mounts, while router.get defines on a router and requires export and app.use for mounting, enabling modular, reusable routes.

Explain that express.Router is a class in Express.js that returns a new router object, with code demonstrating how to define routing for the router method.

Learn how routing and middleware authenticate requests using a token in the request header, protect a route under /api, and respond with unauthorized when the token is missing.

Learn how route chaining in Express.js lets you define multiple middlewares for a single route. Route chaining improves modularity, readability, and separation of concerns by grouping route handlers.