Node.js Interview Questions and Answers
Tags: node, nodejsinterview, interviewquestions, nodeinterview
Published: 2023-05-18 06:05:42

Practice here the most popular [Node.js Interview Questions and Answers](https://www.onlineinterviewquestions.com/node-js-interview-questions/) for Freshers.

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**What is Node.js?**
**Answer:** Node.js is an open-source JavaScript runtime environment that allows developers to run JavaScript on the server-side. It uses an event-driven, non-blocking I/O model, making it lightweight and efficient for building scalable network applications.

**What are the key features of Node.js?**
**Answer:** Some key features of Node.js include:

- Asynchronous and event-driven programming model.
- Single-threaded but highly scalable.
- Non-blocking I/O operations.
- Extensive module ecosystem (npm).
- Fast and efficient execution.

**How does Node.js handle asynchronous programming?**
**Answer:** Node.js uses callbacks, Promises, and async/await syntax to handle asynchronous programming. It leverages an event loop, which allows it to handle multiple concurrent operations without blocking the execution of other code.

**What is npm?**
**Answer:** npm (Node Package Manager) is the default package manager for Node.js. It provides a vast ecosystem of reusable modules and packages that developers can use in their Node.js projects. npm allows easy installation, management, and sharing of packages.

**How can you include external modules in Node.js?**
**Answer:** You can include external modules in Node.js using the require() function. For example, to include the "express" module, you can use const express = require('express');.

**What is the purpose of the package.json file in a Node.js project?**
**Answer:** The package.json file is used to manage a Node.js project. It contains metadata about the project, such as dependencies, scripts, version information, and other configuration details. It also allows you to define scripts for tasks like running tests or starting the application.

**How can you handle errors in Node.js?**
**Answer:** In Node.js, you can handle errors using try/catch blocks or by using error-first callbacks. Additionally, you can use the error event for error handling in streams and utilize the Promise API for handling asynchronous errors.

**What is the purpose of the Express.js framework?**
**Answer: **Express.js is a popular web application framework for Node.js. It provides a set of features and tools to build web applications and APIs easily. It simplifies routing, middleware handling, and request/response handling, making it a popular choice for building web servers in Node.js.

**What are streams in Node.js?**
**Answer:** Streams are objects used to handle streaming data in Node.js. They allow you to read or write data in chunks, which is especially useful for large data sets. Streams provide efficient memory usage and enable processing of data in real-time as it becomes available.

**What is the difference between Node.js and JavaScript?**
**Answer:** JavaScript is a programming language, whereas Node.js is a runtime environment that allows JavaScript to be executed outside of a web browser. Node.js provides additional features and APIs, such as file system access and networking capabilities, that are not available in traditional browser-based JavaScript.

**How can you handle file operations in Node.js?**
**Answer:** Node.js provides the fs module for file system operations. You can use it to read files, write files, create directories, delete files, and perform other file-related tasks. The fs module supports both synchronous and asynchronous operations.

**What is middleware in Express.js?**
**Answer:** Middleware in Express.js refers to functions that have access to the request and response objects in an Express application's request-response cycle. It allows you to add custom logic and perform operations on the request and response, such as authentication, logging, data parsing, and error handling.

**What is the purpose of the module.exports in Node.js?**
**Answer:** module.exports is a special object in Node.js that defines the public API of a module. It is used to export functions, objects, or values from a module so that other modules can use them. By assigning values to module.exports, you make them accessible to other modules through the require() function.

**How can you handle form data in Express.js?**
**Answer:** Express.js provides middleware called body-parser to handle form data. It can parse URL-encoded and JSON data submitted via HTML forms. You can use body-parser by installing it through npm and then including it as middleware in your Express application.

**What is the purpose of the EventEmitter class in Node.js?**
**Answer:**The EventEmitter class is a core module in Node.js that allows objects to emit and listen for events. It provides an implementation of the observer pattern, allowing communication between different parts of an application. You can create custom event emitters and listen for specific events using the on() method.

**What is callback hell, and how can it be avoided?**
**Answer:** Callback hell refers to the situation where deeply nested and chained callbacks make the code difficult to read and maintain. It often occurs when dealing with asynchronous operations. To avoid callback hell, you can use techniques like modularization, Promises, or async/await syntax, which provide cleaner and more readable code.

**Explain the concept of non-blocking I/O in Node.js.**
**Answer:** Non-blocking I/O is a key feature of Node.js that allows it to handle multiple I/O operations concurrently without blocking the execution of other code. Instead of waiting for an I/O operation to complete, Node.js continues executing other tasks. When an I/O operation finishes, a callback function is triggered to handle the result.

**What are the benefits of using npm in Node.js?**
**Answer:** npm offers several benefits, including:

- Easy installation and management of third-party packages and libraries.
- Simplified dependency management with the ability to specify and update package versions.
- A vast ecosystem of open-source modules and tools to leverage in your projects.
- Simple command-line interface for running scripts, testing, and building applications.

**How can you handle sessions in Express.js?**
**Answer:** Express.js does not provide built-in session handling. However, you can use middleware packages like express-session or cookie-session to manage sessions in your Express application. These middleware modules handle session data, session cookies, and session storage for you.

Remember to thoroughly prepare for your Node.js interview by studying the core concepts, exploring sample projects.
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Also, Practice [Node.js MCQ Questions](https://www.onlineinterviewquestions.com/node-js-quiz/).