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## What **npm** is

**npm** stands for

> **Node Package Manager** - *the package manager for Node.js.*

### In other words:

> npm is a tool that lets you **install, update, remove and manage** libraries (packages) in Node.js projects.

## Main npm functions

| Capability | What it does |
|---|---|
| Installing packages | Installs external libraries (`npm install express`) |
| Publishing packages | Lets you publish your own package to the public npm registry |
| Managing dependencies | Tracks versions, stores them in `package.json` |
| Running scripts | Lets you run commands from the `scripts` section |
| Caching | Stores downloaded packages locally, speeding up reinstalls |

## Example npm commands

| Command | Purpose |
|---|---|
| `npm init` | Creates `package.json` |
| `npm install` (or just `npm i`) | Installs all dependencies from `package.json` |
| `npm install express` | Installs a specific package |
| `npm install --save-dev nodemon` | Installs a package as a dev dependency |
| `npm uninstall express` | Removes a package |
| `npm update` | Updates dependencies |
| `npm run <script>` | Runs a command from `"scripts"` in `package.json` |
| `npm publish` | Publishes your own package to the npm registry |

## Where packages are stored after installing

All packages installed via npm land in the `node_modules/` folder
at the project root.

## What `node_modules` is

`node_modules` is the **directory** where npm (or pnpm, yarn) installs **all of a project's dependencies**.

### Example project structure

```javascript
my-app/
├── node_modules/
│   ├── express/
│   ├── chalk/
│   ├── lodash/
│   └── ...
├── package.json
├── package-lock.json
└── index.js
```

Each installed package is a folder inside `node_modules`.

## How npm and node_modules relate

1. When you install a package:

```javascript
npm install express
```

2. npm:

- looks up the package **in the online npm registry** ([https://www.npmjs.com](https://www.npmjs.com)),
- downloads it and all of its dependencies,
- places everything in the `node_modules/` folder,
- records the name and version in `package.json`.

## What `package-lock.json` is

After installing, npm creates a `package-lock.json` file:

- it pins the **exact versions** of every installed package and its sub-dependencies;
- it guarantees an **identical install** for every developer on the project;
- it speeds up repeat installs.

## Example process

```javascript
npm init -y          # create package.json
npm install express  # install the library
```

After that, the structure:

```javascript
my-app/
├── node_modules/
│   └── express/
├── package.json
└── package-lock.json
```

## Important details

### Local vs global packages

| Type | Command | Where it's installed |
|---|---|---|
| **Local** | `npm install express` | into `./node_modules` of the current project |
| **Global** | `npm install -g nodemon` | into npm's external system directory |

### Why `node_modules` is needed

- It is the **physical storage** for all of a project's dependencies.
- Without it, the project won't run if dependencies aren't installed.

### Why `node_modules` is not committed to GitHub

The folder can take up **hundreds of megabytes**.
Instead, only these are added to the repository:

- `package.json`, the list of dependencies;
- `package-lock.json`, the exact versions.

When cloning a project, it's enough to run:

```javascript
npm install
```

and npm recreates `node_modules` from scratch.

## Summary

| Concept | Description |
|---|---|
| **npm** | The package manager for Node.js (installs, updates, publishes libraries) |
| **node_modules** | The folder where installed packages physically live |
| **package.json** | Describes a project's dependencies |
| **package-lock.json** | Pins exact package versions for stability |

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