Top 10 node js interview questions and answer

Umar Farooque Khan
5 min readJun 14, 2023

Node.js interview questions along with their answers and examples:

  1. What is Node.js and how does it differ from traditional JavaScript?

Node.js is a server-side JavaScript runtime environment. It allows running JavaScript code outside of a web browser. Unlike traditional JavaScript, which runs in the browser, Node.js enables JavaScript to be executed on the server, making it suitable for building scalable and efficient web applications.

2. What is npm? How does it work and why is it important in Node.js?

npm (Node Package Manager) is the default package manager for Node.js. It allows developers to discover, install, and manage packages and dependencies for their Node.js projects. npm simplifies the process of sharing and reusing code, promoting modularity and efficiency in Node.js development.

Example:
To install a package using npm, you can run the following command:

npm install

3. Explain the concept of event-driven programming in Node.js.

In Node.js, event-driven programming is based on the concept of event emitters and event listeners. It allows asynchronous, non-blocking execution of code. Event emitters emit events, and event listeners are registered to listen for those events. When an event is emitted, the associated listener(s) are triggered, allowing for reactive and scalable application development.

Example:

event-driven programming in Node.js.

4. What is Express.js and how does it relate to Node.js?

Express.js is a popular web application framework built on top of Node.js. It provides a set of features and utilities to simplify web development, such as routing, middleware support, and template engines. Express.js enhances the capabilities of Node.js, making it easier to build robust and scalable web applications.

Example: Setting up a basic Express.js server:

5. How does Node.js handle asynchronous operations? Explain the event loop.

Node.js uses an event-driven, non-blocking I/O model to handle asynchronous operations. The event loop is a key component in this process. It continuously checks for new events and executes their associated callbacks when they occur. This allows Node.js to handle multiple concurrent operations efficiently.

  • Example: Reading a file asynchronously using the fs module:

6. What are streams in Node.js and how are they useful?

Streams are a fundamental concept in Node.js that allow reading from or writing to a source of data continuously. They enable efficient handling of large data sets, as data is processed in chunks rather than loading the entire dataset into memory. Streams are useful for tasks like file I/O, network communication, and data transformation.

Example: Piping data from a readable stream to a writable stream:

7. What is middleware in the context of Node.js and Express.js?

Middleware in Node.js and Express.js refers to functions that have access to the request and response objects in the application’s middleware stack. They can perform various tasks, modify request/response objects, or terminate the request-response cycle. Middleware allows for modular and reusable code, and it plays a crucial role in handling routes, authentication, error handling, etc.

Example: A simple middleware function that logs the request URL:

middleware function

8. Explain the purpose and usage of package.json in Node.js.

The package.json file is a manifest for a Node.js project. It holds metadata about the project, including its dependencies, scripts, version, author, and more. It allows developers to define project configurations, manage dependencies, and automate tasks using scripts. The package.json file is crucial for sharing and reproducing Node.js projects.

Example: An example package.json file:

Example of package.json

9. How can you handle errors in Node.js applications?

In Node.js, errors can be handled using try-catch blocks for synchronous code or using error-first callbacks or promises for asynchronous code. Additionally, Node.js provides a global uncaughtException event for handling uncaught exceptions. Proper error handling ensures graceful application termination and effective debugging.

  • Example: Error handling with try-catch block:

10. What are the differences between spawn, fork, and exec in the child_process module of Node.js?

The spawn, fork, and exec methods in the child_process module are used to create child processes in Node.js. They have different use cases:

  • spawn: Used to create a new process and communicate with it using streams. It is suitable for long-lived processes or when streaming large amounts of data.
  • fork: A variation of spawn specifically designed for creating child processes that run Node.js modules. It facilitates inter-process communication through a messaging channel.
  • exec: Used to execute a command in a shell. It buffers the command's output and provides a callback when the command completes.

Executing a command using exec:

These questions cover various important aspects of Node.js, including its fundamentals, key.

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Umar Farooque Khan

Experienced software developer with a passion for clean code and problem-solving. Full-stack expertise in web development. Lifelong learner and team player.