Node.js Basics›Core· 35 min read

NPM & package.json

Tap into millions of free packages and manage your project with npm — the world’s largest software library.

What you will learn

Initialise a project with package.json
Install and use packages
Understand dependencies and scripts

Start a project

npm (Node Package Manager) comes free with Node. It is like an app store for code: millions of ready-made packages you can drop into your project in seconds. Every npm project starts with a package.json file — your project’s ID card, listing its name, version, scripts and the packages it depends on.

Using a package is a simple three-step flow:

Create package.json with npm init -y — this is the file that will remember every package you add.
Install a package with npm install <name> — npm downloads it into a node_modules folder and records it in package.json.
Use it in your code with require("<name>"), exactly like a built-in module.

Terminal: start a project and install a package

npm init -y          # create package.json
npm install dayjs    # install a package (adds it to dependencies)

Note: Output: Wrote to /your/project/package.json ... added 1 package in 1s npm init -y creates package.json instantly (the -y means "yes to all the default questions"). npm install dayjs then downloads the popular dayjs date library, drops its code into node_modules/, and adds a line for it under "dependencies" in package.json so the project remembers it.

Use an installed package

Once installed, you bring the package in with require — the same way you imported your own modules, but using just its name (no ./ ), because it lives in node_modules:

Require and use the installed package

// app.js
const dayjs = require("dayjs");
console.log("Today is", dayjs().format("DD MMM YYYY"));

Note: Output: Today is 07 Jun 2026 require("dayjs") loads the installed library. Calling dayjs() makes an object for today’s date, and .format("DD MMM YYYY") turns it into a tidy string — DD is the day, MMM the short month name, YYYY the four-digit year. You wrote three lines and got date formatting that would take many lines by hand.

What gets created

Thing	What it is
`package.json`	Project info + list of dependencies
`package-lock.json`	Exact versions installed (do not edit)
`node_modules/`	The downloaded package code (never commit it)

Watch out: Never commit node_modules/ to git — it is huge and rebuildable. Add it to .gitignore. Anyone can recreate it with npm install using your package.json.

Scripts

Typing long commands again and again is tedious. Scripts let you save a command under a short name inside package.json (in the "scripts" section), then run it with npm run <name>. The dev tool nodemon auto-restarts your server every time you save a file.

npm scripts

// package.json
"scripts": {
  "start": "node app.js",
  "dev": "nodemon app.js"
}

Note: Output: (no output — this is configuration) This adds two shortcuts. Now npm start runs node app.js (the start name is special, so you can drop the run), and npm run dev runs nodemon app.js. You type a short, memorable command and npm runs the long one for you.

Q. Which file lists your project’s dependencies?

Answer: package.json records your dependencies (and scripts). npm install reads it to download the packages into node_modules.

✍️ Practice

Run npm init -y, install a package, and use it in a script.
Add a "start" script to package.json and run it with npm start.

🏠 Homework

Create a project, install nodemon as a dev dependency, and add a dev script that uses it.