NPM & package.json

npm (Node Package Manager) ships with Node itself, and package.json is the file that describes your project — its dependencies, its scripts, and basic metadata.

Starting a project

bash terminal

npm init -y

Generated package.json

{
  "name": "my-app",
  "version": "1.0.0",
  "main": "index.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  }
}

The -y flag accepts all the defaults instead of asking a series of questions — fine for getting started, easy to edit afterward.

Installing a package

bash terminal

npm install express

Output

added 64 packages in 2s

This creates a node_modules folder (the actual package code), a package-lock.json (exact installed versions, for reproducible installs), and adds an entry to package.json:

package.json, after install

"dependencies": {
  "express": "^4.19.2"
}

npm scripts

The scripts section defines shortcuts you run with npm run (or just npm start/npm test for those two specific names):

JSON package.json (scripts section)

"scripts": {
  "start": "node index.js",
  "dev": "node --watch index.js"
}

bash terminal

npm start

Output

> my-app@1.0.0 start
> node index.js

Server running at http://localhost:3000/

Note: node_modules should never be committed to git — it can be entirely regenerated from package.json and package-lock.json with npm install, and it's often huge. package-lock.json, on the other hand, should be committed — it's what guarantees everyone on a team, and your production server, installs the exact same dependency versions.

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