What is npm and why use it?

📦 What is `npm`?

npm stands for Node Package Manager.
It's the default package manager bundled with Node.js — installing Node automatically gives you npm.
Lets you install, manage, update, and share reusable code, called "packages" or "modules."

🧠 Think of it as a massive online registry of libraries and tools built by other developers, ready to plug into your app instead of building everything yourself.

⚙️ What npm Actually Does

Installs packages — pulls code from the npm registry into your project.
Tracks versions — records exactly which version of each package your project uses.
Manages dependencies — handles the web of packages-that-depend-on-other-packages automatically.
Runs scripts — lets you define custom commands (like npm start or npm run build) in package.json.

🤔 Why Use npm?

Avoid reinventing the wheel — use express instead of writing a full server from scratch.
Share your own libraries — publish your own packages for others (or your future self) to reuse.
Easily manage project dependencies — one file (package.json) tracks everything your project needs.
Stay up to date — update packages and pull in bug fixes or new features with a single command.

🌐 npm Has Three Parts

The registry — the online database where packages live (like github)
The CLI — the npm command you run in your terminal.
The website — npmjs.com, where you can browse and search packages.

📦 Types of Packages in Node.js

Not every require() in your code pulls from the internet. Node draws from three different sources, depending on what you're importing.

Ship with Node.js itself — no installation needed.
Provide low-level functionality like file access, networking, and cryptography.
Imported by name only, with no path or npm install.

const fs = require('fs');
const http = require('http');
const path = require('path');

Examples: fs, http, path, os, crypto, events, util.
💡 Node checks these first — if the name matches a core module, it never touches node_modules/.

Written by other developers and published to the npm registry.
Must be installed first, then imported by name.

npm install lodash

const _ = require('lodash');

Live inside node_modules/ and get listed in package.json.
Examples: lodash, express, axios, dotenv.

Files you write yourself, as part of your own project.
Imported using a relative path — never a bare name — so Node knows to look on disk, not in node_modules/.

// utils.js
function greet(name) {
  return `Hello, ${name}!`;
}
module.exports = { greet };

// index.js
const { greet } = require('./utils');
console.log(greet('Bhaskar'));

The ./ prefix is what tells Node "this is a local file," not a package to look up.
Great for splitting your own code into organized, reusable pieces.

🧭 How Node Decides Where to Look

When you call require('something'), Node checks in this order:

Is it a core module? (fs, path, etc.) → use the built-in one.
Does the path start with ./ or ../? → treat it as your own local file.
Otherwise → search node_modules/ for a matching external package.

📦 What is npm?