1. What is npm?

npm stands for Node Package Manager. It's the default package manager for Node.js.
It helps developers install, share, and manage dependencies in their Node.js projects.
It provides access to the npm registry, a vast collection of reusable packages.

2. Setting Up npm

A. Installing Node.js

npm comes bundled with Node.js.
Download and install Node.js from the official site.

B. Verifying Installation

Check the installed versions:

node -v  # Check Node.js version
npm -v   # Check npm version

3. Initializing a Project

A. Creating a `package.json` File

The package.json file is the heart of your Node.js project, storing metadata about the project and its dependencies.

Run:

npm init

You’ll be prompted for details like the project name, version, description, etc. Add -y to skip the prompts and create a default package.json:

npm init -y

Example package.json:

{
  "name": "my-project",
  "version": "1.0.0",
  "description": "A sample project",
  "main": "index.js",
  "scripts": {
    "start": "node index.js"
  },
  "dependencies": {},
  "devDependencies": {}
}

4. Installing Packages

A. Installing a Single Package

To install a package (e.g., lodash):

npm install lodash

This adds lodash to your dependencies in package.json and stores it in the node_modules folder.

B. Installing Development Dependencies

For packages needed only during development (e.g., testing libraries):

npm install jest --save-dev

C. Global Installation

For tools used across projects (e.g., nodemon):

npm install -g nodemon

D. Installing Specific Versions

npm install express@4.17.1

5. Dependency Management

A. Semantic Versioning (SemVer)

npm uses SemVer for versioning:

^1.2.3: Allows minor and patch updates (e.g., 1.3.0, 1.2.4).
~1.2.3: Allows only patch updates (e.g., 1.2.4).
1.2.3: Installs exactly this version.

B. `package-lock.json`

This file locks the exact versions of dependencies installed, ensuring consistency across environments.

6. Useful npm Commands

A. Viewing Installed Packages

npm list        # Lists installed dependencies
npm list -g     # Lists globally installed packages

B. Updating Packages

npm update      # Updates all dependencies
npm update lodash  # Updates a specific package

C. Removing Packages

npm uninstall lodash

D. Cleaning Up

Remove unused dependencies:

npm prune

7. Scripts in npm

The scripts section in package.json lets you define custom commands:

"scripts": {
  "start": "node index.js",
  "test": "jest"
}

Run a script:

npm run start
npm run test

8. Creating Your Own npm Package

A. Step 1: Prepare the Project

Initialize the project:
```
 npm init
```

Write your code:

 // index.js
 module.exports = {
     greet: (name) => `Hello, ${name}!`
 };

B. Step 2: Add Metadata

Ensure package.json has a proper name, version, and description.

C. Step 3: Publish the Package

Log in to npm:
```
 npm login
```
Publish your package:
```
 npm publish
```

D. Install Your Published Package

npm install your-package-name

9. Managing npm Configurations

A. View and Edit npm Config

npm config list
npm config set init-author-name "Your Name"
npm config delete init-author-name

B. Use `.npmrc`

Add custom configurations:

registry=https://registry.npmjs.org/

10. Security Best Practices

A. Check for Vulnerabilities

npm audit
npm audit fix

B. Avoid Installing Untrusted Packages

Review package popularity and code before installing.
Avoid globally installing unknown packages.

11. Troubleshooting npm

A. Clearing npm Cache

npm cache clean --force

B. Fixing Permissions Issues

Use npx for isolated environments:

npx create-react-app my-app

12. Advanced npm Concepts

A. Workspaces

Workspaces allow managing multiple packages in a single project.

Create a package.json with:

 {
     "workspaces": ["packages/*"]
 }

Add sub-packages under packages/.

B. Package Bundlers

Use tools like webpack or esbuild to bundle your npm packages for production.

Learn about npm: Step-by-Step Guide to Node Package Manager