Question 1

What is Node.js?

Accepted Answer

Node.js is a cross-platform, open-source JavaScript runtime environment that executes JavaScript code outside a web browser. It is built on Google Chrome's V8 JavaScript engine.

Question 2

Is Node.js single-threaded?

Accepted Answer

Yes, Node.js is primarily single-threaded for its event loop, but it uses internal worker threads (via libuv) for handling expensive I/O operations like file system access or network requests.

Question 3

What is the difference between Node.js and JavaScript?

Accepted Answer

JavaScript is a programming language, whereas Node.js is a runtime environment that allows you to run JavaScript on the server side.

Question 4

What is npm?

Accepted Answer

npm (Node Package Manager) is the default package manager for Node.js. It allows developers to share and reuse code and manage project dependencies.

Question 5

What is REPL in Node.js?

Accepted Answer

REPL stands for Read-Eval-Print Loop. It is an interactive shell that takes user inputs, executes them, and prints the result, useful for testing small snippets of code.

Question 6

What are the core modules of Node.js?

Accepted Answer

Core modules include 'fs' (file system), 'http' (creating servers), 'path' (handling file paths), 'os' (operating system info), and 'events' (event emitters).

Question 7

How do you create a simple server in Node.js?

Accepted Answer

Using the 'http' module: `http.createServer((req, res) => { res.end('Hello'); }).listen(3000);`

Question 8

What is the role of 'package.json'?

Accepted Answer

It is the manifest file for a Node.js project. It contains metadata about the project, script definitions, and lists of dependencies and devDependencies.

Question 9

What is the difference between `require` and `import`?

Accepted Answer

`require` is CommonJS syntax used in Node.js by default. `import` is ES6 module syntax. Node.js supports both, but ES6 requires `.mjs` extension or `"type": "module"` in package.json.

Question 10

What is a callback function?

Accepted Answer

A callback is a function passed as an argument to another function, which is executed after some operation (usually asynchronous) is completed.

Question 11

What is the Event Loop in Node.js?

Accepted Answer

The Event Loop is a mechanism that allows Node.js to perform non-blocking I/O operations by offloading tasks to the system kernel whenever possible.

Question 12

What is the difference between `setImmediate()` and `setTimeout()`?

Accepted Answer

`setImmediate()` is designed to execute a script once the current poll phase completes. `setTimeout()` schedules a script to be run after a minimum threshold in ms has elapsed.

Question 13

What is the purpose of `module.exports`?

Accepted Answer

It is used to define what a module exports so that it can be used in other files using `require()`.

Question 14

What is `process.argv`?

Accepted Answer

It is an array containing the command-line arguments passed when the Node.js process was launched.

Question 15

Explain 'Non-blocking I/O'.

Accepted Answer

It means that Node.js doesn't wait for an I/O operation (like reading a file) to finish before moving to the next task. Instead, it provides a callback.

Question 16

What is the `fs` module?

Accepted Answer

The `fs` (File System) module allows you to interact with the file system on your computer (reading, writing, deleting files).

Question 17

What is 'Callback Hell'?

Accepted Answer

It occurs when multiple nested callbacks make the code hard to read and maintain. It's often solved using Promises or Async/Await.

Question 18

What is a Promise?

Accepted Answer

A Promise is an object representing the eventual completion (or failure) of an asynchronous operation and its resulting value.

Question 19

What is Async/Await?

Accepted Answer

It is a syntactic sugar built on top of Promises that allows you to write asynchronous code that looks and behaves like synchronous code.

Question 20

What is Global Object in Node.js?

Accepted Answer

Unlike the browser's `window` object, Node.js has a `global` object. Common globals include `process`, `__dirname`, and `__filename`.

Question 21

Explain `__dirname` and `__filename`.

Accepted Answer

`__dirname` is the directory name of the current module. `__filename` is the absolute path of the current module file.

Question 22

What is the use of 'path' module?

Accepted Answer

The 'path' module provides utilities for working with file and directory paths (e.g., `path.join()`, `path.extname()`).

Question 23

What is 'error-first callback'?

Accepted Answer

It is a pattern where the first argument of a callback is an error object (if any), and the second argument is the result data.

Question 24

How do you install a specific version of a package?

Accepted Answer

Using `npm install @` (e.g., `npm install express@4.17.1`).

Question 25

What is the difference between `dependencies` and `devDependencies`?

Accepted Answer

`dependencies` are required for the application to run. `devDependencies` are only needed for development and testing (e.g., nodemon, jest).

Question 26

What is 'nodemon'?

Accepted Answer

Nodemon is a tool that automatically restarts the Node.js application when file changes in the directory are detected.

Question 27

What is 'event-driven' programming?

Accepted Answer

It is a paradigm where the flow of the program is determined by events such as user actions, sensor outputs, or messages from other programs.

Question 28

What is an EventEmitter?

Accepted Answer

A class in the 'events' module used to handle custom events. You can 'emit' events and 'listen' for them using `.on()`.

Question 29

What is a Buffer in Node.js?

Accepted Answer

A Buffer is a way to handle binary data in Node.js, specifically used to deal with streams of binary data.

Question 30

What is the purpose of `os` module?

Accepted Answer

The `os` module provides operating system-related utility methods like `os.platform()`, `os.cpus()`, and `os.totalmem()`.

Node.js Backend Interview Master

Difficulty Filters

Tools & Options

What is Node.js?

Is Node.js single-threaded?

What is the difference between Node.js and JavaScript?

What is npm?

What is REPL in Node.js?

What are the core modules of Node.js?

How do you create a simple server in Node.js?

What is the role of 'package.json'?

What is the difference between `require` and `import`?

What is a callback function?

What is the Event Loop in Node.js?

What is the difference between `setImmediate()` and `setTimeout()`?

What is the purpose of `module.exports`?

What is `process.argv`?

Explain 'Non-blocking I/O'.

What is the `fs` module?

What is 'Callback Hell'?

What is a Promise?

What is Async/Await?

What is Global Object in Node.js?

Explain `__dirname` and `__filename`.

What is the use of 'path' module?

What is 'error-first callback'?

How do you install a specific version of a package?

What is the difference between `dependencies` and `devDependencies`?

What is 'nodemon'?

What is 'event-driven' programming?

What is an EventEmitter?

What is a Buffer in Node.js?

What is the purpose of `os` module?

What is 'Stream' in Node.js?

Name the types of Streams in Node.js.

What is 'piping' in streams?

What is 'Chaining' in Node.js?

What is the use of `util.promisify()`?

What is 'Express.js'?

What is 'Middleware' in Express?

How do you handle routing in Express?

What is 'body-parser'?

What is 'REST API'?

What is 'JSON'?

Explain `cors` package.

What is `dotenv`?

What is 'Mongoose'?

What is 'JWT'?

How to handle file uploads in Node.js?

What is 'Bcrypt' used for?

What is 'Validation' in Node.js API?

What is the difference between `null` and `undefined` in JS?

What is 'Hoisting'?

Explain the Event Loop phases.

What are 'Microtasks' and 'Macrotasks'?

What is `process.nextTick()`?

How does Node.js handle concurrency?

Explain 'Clustering' in Node.js.

What is 'Worker Threads' module?

Difference between Cluster and Worker Threads?

How to handle memory leaks in Node.js?

Explain 'Backpressure' in Streams.

What is 'libuv'?

How to secure a Node.js API?

Explain 'authentication' vs 'authorization'.

How to scale Node.js applications?

What is 'PM2'?

Explain 'Socket.io'.

What is 'Redis' used for in Node.js?

Explain 'Stub', 'Mock', and 'Spy' in testing.

How to perform 'Graceful Shutdown'?

Explain 'Domain-Driven Design' (DDD) in Node.js.

What is 'Microservices Architecture'?

How to handle distributed tracing?

Explain 'Event Sourcing'.

What is 'CQRS'?

How to optimize expensive database queries?

Explain 'Hydration' in Node.js SSR.

How to handle 10k connections simultaneously?

Explain 'Garbage Collection' in V8.

Explain `dirname` and `filename`.