Top Node.js Modules Interview Questions and Answers for 2023

Node.js has become one of the most popular backend technologies over the past few years. Its event-driven, non-blocking I/O model makes it perfect for building scalable network applications. As a result, there is huge demand for Node.js developers and knowing Node.js modules is a must for any aspiring Node.js developer. In this article, we will look at some of the most frequently asked Node.js modules interview questions and sample answers to help you prepare.

What are Modules in Node.js?

Modules in Nodejs are reusable pieces of code in a JavaScript file that can be imported and used in other Nodejs files. Each module in Node.js has its own context and allows encapsulation of related code into one unit. Some advantages of using modules in Node.js are

• Modularization of code into logical units
• Reusability of code across files/projects
• Namespacing – avoids variable name collisions
• Maintainability – easy to manage codebase
• Encapsulation – hide implementation details

Node.js has a simple module loading system that allows modules to be loaded using the require() function. Some of the core modules in Node.js include http, fs, path etc. Npm packages installed can also be loaded as modules.

Explain require() in Node.js?

The require() function is used to import and load modules in Nodejs It takes the module name/path as an argument and returns the exported API of that module. Some key points about require()

• Used to import local modules as well as core Node.js modules
• Modules are cached after first load so subsequent calls are faster
• Can load JSON files and npm packages directly
• require() calls are synchronous but the modules can work asynchronously
• Paths are relative to current file, absolute paths can also be used
• Folders are treated as modules, index.js file is loaded by default

Here is an example usage of require():

// Load a local moduleconst myModule = require('./myModule'); // Load core moduleconst http = require('http');// Load package module const moment = require('moment'); 

What is the module.exports property in Node.js?

The module.exports property is used to export an API from a Node.js module so that it can be imported and used in other files using require(). Anything assigned to module.exports becomes publicly available from that module.

For example:

// myModule.jsconst message = "Hello World";function printMessage() {  console.log(message);}module.exports.message = message; module.exports.printMessage = printMessage;

We can now import myModule in another file and access the exported API:

const myModule = require('./myModule');myModule.message; // "Hello World" myModule.printMessage(); // prints "Hello World"

How does Node.js handle module caching?

Node.js caches modules after the first time they are loaded using require(). This significantly improves performance by avoiding reloading of modules.

The caching is done based on the module’s absolute file path. So any subsequent calls to require() the same module path will get the cached version instead of re-loading the file.

This caching behavior allows reuse of already initialized modules between different modules in a Node.js application.

The module caching can be bypassed by calling require() with an additional parameter:

// Force reload module const myModule = require('./myModule', {cache: false}); 

What is the package.json file in Node.js?

The package.json file contains metadata for a Node.js project or module. It includes information like the project name, version, dependencies, build scripts etc. The main purposes of package.json are:

• Specifies project dependencies and devDependencies
• Defines entry points like main, scripts etc
• Stores metadata like project name, version, author etc.
• Used by npm for managing dependencies and packages
• Can define command line scripts for build automation
• Required for publishing packages to npm registry

Here is an example package.json:

{  "name": "my-project",  "version": "1.0.0",  "description": "My Node.js project",   "main": "app.js",  "scripts": {    "start": "node app.js"  },  "dependencies": {    "express": "^4.17.1"   },  "devDependencies": {    "jest": "^26.6.3"   } }

How to create a Node.js module?

There are two ways to create a Node.js module:

1. Create a JavaScript file and export API using module.exports

For example:

// myModule.jsconst X = {};X.hello = function() {  return 'Hello';}module.exports = X;

1. Create a folder with an index.js file that exports API:

/myModule  index.js

Inside index.js:

const X = {};// exportsmodule.exports = X; 

We can now require() myModule from other files to use its API.

What is NPM and what is it used for?

NPM stands for Node Package Manager. It is the default package manager for Node.js and is used to install, update, configure and manage dependencies in a Node.js application.

Some of the key features and uses of NPM are:

• Online repository of published open source Node.js projects/modules
• Dependency management for Node.js projects
• Installs modules from npm registry using npm install
• Manages versioning and dependencies of modules
• Handles dependencies between modules using a package.json file
• Can execute scripts defined in package.json
• CLI tool to publish, discover, install Node.js modules

NPM makes it easy to reuse common modules across different Node.js projects. The huge npm registry has over 1.5 million modules as of 2022.

How does NPM handle dependency versioning?

NPM uses semantic versioning (semver) to manage dependencies between modules/packages. This helps avoid version conflicts.

Semantic version numbers take the form X.Y.Z:

• X – Major version
• Y – Minor version
• Z – Patch

Rules:

• Patch releases contain only bug fixes, no API changes
• Minor releases can add functionality in a backwards-compatible way
• Major releases can make incompatible API changes

NPM uses version ranges to specify acceptable dependency versions:

"MODULE": "1.2.x" // Permits any 1.2 release"MODULE": "~1.2.3" // Permits patch-level changes"MODULE": "^1.2.3" // Permits minor-level changes

So NPM can install the best matching version range for dependencies.

What is the node_modules folder?

The node_modules folder contains installed dependencies for a Node.js project. NPM installs all packages defined in the dependencies section of package.json into this folder.

Some key points about node_modules:

• Created by NPM when you run npm install
• Contains all installed dependencies for the project
• Should be excluded from source control, can be recreated based on package.json
• Nesting – modules can have their own node_modules folders
• NPM looks in node_modules when resolving require()

Node.js will look in the node_modules folders up the directory tree to resolve imported modules. Having all dependencies in one place avoids versioning conflicts.

What is Semantic Versioning in NPM?

Semantic Versioning (SemVer) is a convention NPM uses to manage version numbers for packages/modules. SemVer version numbers take the form MAJOR.MINOR.PATCH:

• MAJOR – Incremented for incompatible API changes
• MINOR – Incremented for new backwards-compatible functionality
• PATCH – Incremented for bug fixes

Additionally, NPM allows version ranges when specifying dependencies:

• ~1.2.3 – Allows patch releases (1.2.x)
• ^1.2.3 – Allows minor releases (1.x.x)
• 1.2.x – Allows patch and minor releases

This provides flexibility when depending on modules while avoiding major version conflicts. SemVer enables robust dependency management for Node.js projects.

Explain the event loop in Node.js

The event loop is the secret behind Node.js’ efficient non-blocking I/O operations even though JavaScript is single-threaded. Here is how it works:

• Node.js maintains an event queue for pending async operations like file I/O
• When an async operation is initiated, it gets added to the queue
• The event