NPM in Node.js

NPM stands for Node Package Manager. It is commonly used to install, manage, and share packages that developers use in Node.js projects.

Packages provide reusable code that helps developers build applications without writing every feature from scratch. For example, Express.js helps us create web servers and APIs.

What Is NPM?

NPM is the package manager commonly used in Node.js projects. It provides a command-line tool and an online package registry containing reusable JavaScript packages.

Why Do We Use NPM?

Step 1: Check the NPM Version

First, make sure Node.js and NPM are installed on your computer. Open Command Prompt or a terminal and enter:

npm -v

Example Output

10.9.2

This is an example version number. Your installed version may differ.

Step 2: Create a Project Folder

Create a folder named MyNpmProject and open it in your code editor.

MyNpmProject/

Step 3: Initialize an NPM Project

Before installing project dependencies, you can initialize your project with the following command:

npm init

NPM asks questions about your project, such as its name, version, description, and entry point. Your answers are used to create a package.json file.

Quick Initialization

To create a default package.json without answering each question, use:

npm init -y

Example Project Structure

MyNpmProject/
└── package.json

What Is package.json?

The package.json file contains information about your project, including its name, version, scripts, and dependencies.

{
  "name": "my-npm-project",
  "version": "1.0.0",
  "description": "My first NPM project",
  "main": "app.js",
  "scripts": {
    "start": "node app.js"
  }
}

This is a simplified example. NPM can create a similar file automatically when you initialize a project.

Step 4: Install a Package

Let's install a package named lodash. Lodash provides utility functions for working with JavaScript values and collections.

npm install lodash

After installation, your project will normally contain:

MyNpmProject/
├── node_modules/
├── package.json
└── package-lock.json

• node_modules/ contains installed packages and their dependencies.
• package.json records project details and dependency declarations.
• package-lock.json records the resolved dependency versions for reproducible installations.

Step 5: Use an Installed Package

After installing Lodash, create a file named app.js in your project folder.

const _ = require("lodash");

const numbers = [10, 20, 30, 40];

console.log(_.sum(numbers));

Run the Program

node app.js

Output

100

Explanation

• require("lodash") loads the installed Lodash package in this CommonJS example.
• numbers stores an array of numbers.
• _.sum(numbers) calculates the sum of the array values.
• console.log() displays the result.

Step 6: Install a Development Dependency

Some packages are needed during development but not when the application is running in production. These can be installed as development dependencies.

npm install --save-dev nodemon

Nodemon can restart a Node.js application when it detects file changes. It is commonly used during development.

Step 7: Uninstall a Package

If you no longer need a package, you can remove it from your project.

npm uninstall lodash

NPM removes the package and updates the project's dependency information.

Useful NPM Commands

Practical Assignment