Node.js NPM

What Is npm?

npm (Node Package Manager) installs alongside Node.js and gives you access to the npm registry, the largest collection of open-source JavaScript packages. It also manages your project's dependencies and defines custom scripts through a single file: package.json. Run npm init to generate one interactively, or npm init -y to accept all the defaults instantly.

{
  "name": "my-node-app",
  "version": "1.0.0",
  "description": "A sample Node.js project",
  "main": "index.js",
  "scripts": {
    "start": "node index.js",
    "test": "echo \"no tests yet\" && exit 0"
  },
  "dependencies": {},
  "devDependencies": {}
}

npm Scripts

// index.js — the script executed by "npm start"
console.log("Server starting...");
console.log("NODE_ENV:", process.env.NODE_ENV || "development");

// package.json: "scripts": { "start": "node index.js" }
// Run with: npm start

Installing Dependencies

Use npm install <package> to add a dependency. npm downloads the package into a node_modules folder, records it in package.json, and locks exact versions in package-lock.json so every machine installs the identical dependency tree.

• npm install express — adds a runtime dependency your app needs to function.
• npm install --save-dev nodemon — adds a devDependency, needed only during development.
• npm install — with no package name, installs everything already listed in package.json.
• npm uninstall <package> — removes a dependency and updates package.json.

Dependencies vs. devDependencies

// version-check.js
const pkg = require("./package.json");

console.log(`${pkg.name} v${pkg.version}`);
console.log("Start script:", pkg.scripts.start);

// Run with: node version-check.js
// Output:
// my-node-app v1.0.0
// Start script: node index.js