NodeJS NPM

NPM (Node Package Manager) is the default package manager for Node.js. It helps manage project dependencies, scripts, and third-party libraries, and is automatically installed when you install Node.js.

• It is mainly used to manage packages or modules, these are pre-built pieces of code that extend the functionality of your NodeJS application.
• The NPM registry hosts millions of free packages that you can download and use in your project.
• NPM is installed automatically when you install NodeJS, so you don’t need to set it up manually.

Package in Node.js

A package in NodeJS is a reusable module of code that adds functionality to your application. It can be anything from a small utility function to a full-featured library.

• Packages can be installed from the NPM registry.
• They are stored in the node_modules folder in your project.
• You can easily install, update, or remove packages with NPM commands.

Using NPM with NodeJS

To start using NPM in your project, follow these simple steps

Step 1: Install NodeJS and NPM

First, you need to install NodeJS. NPM is bundled with the NodeJS installation.

Step 2: Verify the Installation

After installation, verify NodeJS and NPM are installed by running the following commands in your terminal:

node -v
npm -v

These commands will show the installed versions of NodeJS and NPM.

Step 3: Initialize a New NodeJS Project

In the terminal, navigate to your project directory and run:

npm init -y

This will create a package.json file, which stores metadata about your project, including dependencies and scripts.

Step 4: Install Packages with NPM

To install a package, use the following command

npm install <package-name>

For example, to install the Express.js framework

npm install express

This will add express to the node_modules folder and automatically update the package.json file with the installed package information.

Step 5: Install Packages Globally

To install packages that you want to use across multiple projects, use the -g flag:

npm install -g <package-name>

Step 6: Run Scripts

You can also define custom scripts in the package.json file under the "scripts" section. For example:

{
 "scripts": {
 "start": "node app.js"
 }
}

Then, run the script with

npm start

Using NPM Package in the project

Create a file named app.js in the project directory to use the package

• express() creates an instance of the Express app.
• app.get() defines a route handler for HTTP GET requests to the root (/) URL.
• res.send() sends the response “Hello, World!” to the client.
• app.listen(3000) starts the server on port 3000, and console.log() outputs the server URL.

Now run the application with

node app.js

Visit http://localhost:3000 in your browser, and you should see the message: Hello, World!

Managing Project Dependencies

1. Installing All Dependencies

In a NodeJS project, dependencies are stored in a package.json file. To install all dependencies listed in the file, run:

npm install

This will download all required packages and place them in the node_modules folder.

2. Installing a Specific Package

To install a specific package, use:

npm install <package-name>

You can also install a package as a development dependency using:

npm install <package-name> --save-dev

Development dependencies are packages needed only during development, such as testing libraries.

To install a package and simultaneously save it in package.json file (in case using NodeJS), add --save flag. The --save flag is default in npm install command so it is equal to npm install package_name command.

Example:

npm install express --save

Usage of Flags:

• --save: flag one can control where the packages are to be installed.
• --save-prod : Using this packages will appear in Dependencies which is also by default.
• --save-dev : Using this packages will get appear in devDependencies and will only be used in the development mode.

Note: If there is a package.json file with all the packages mentioned as dependencies already, just type npm install in terminal

3. Updating Packages

You can easily update packages in your project using the following command

npm update

This will update all packages to their latest compatible versions based on the version constraints in the package.json file.

To update a specific package, run

npm update <package-name>

4. Uninstalling Packages

To uninstall packages using npm, follow the below syntax:

npm uninstall <package-name>

For uninstall Global Packages

npm uninstall package_name -g

Popular NPM Packages for NodeJS

NPM has a massive library of packages. Here are a few popular packages that can enhance your NodeJS applications

Versioning in NPM

NPM allows you to manage package versions. This is important when you want to ensure that a specific version of a library is used across all environments.

Install a Specific Version

To install a specific version of a package, use:

npm install <package-name>@<version>

For example:

npm install express@4.17.1

This will install version 4.17.1 of Express, regardless of the latest version.

Using Semantic Versioning to manage packages

• To install a specific version, specify the exact version in package.json (e.g., "express": "4.1.1").
• To install the latest version, use "*" or "latest" as the version.
• To install a compatible version above a given version, use the caret (^), e.g., "express": "^4.1.1", which installs a newer compatible version (same major version).

Dependencies Vs DevDependencies