What is npm in Node.js?

Expected Interview Answer

Step-by-Step Explanation

1. Step 1

   Initialize the project

   Run npm init to create a package.json that describes your project and its dependencies.

2. Step 2

   Install a package

   npm install express adds Express to node_modules and lists it under dependencies.

3. Step 3

   Lock the versions

   npm writes package-lock.json recording the exact resolved versions for reproducible installs.

4. Step 4

   Use scripts

   Define scripts in package.json and run them with npm run <name>, e.g. npm run build.

5. Step 5

   Restore anywhere

   On another machine, npm install reads package.json and the lock file to recreate node_modules exactly.

Code Example

{
  "name": "my-app",
  "version": "1.0.0",
  "scripts": {
    "start": "node index.js",
    "test": "jest"
  },
  "dependencies": {
    "express": "^4.19.2"
  },
  "devDependencies": {
    "jest": "^29.7.0"
  }
}

// Install all dependencies listed in package.json
// $ npm install

// Add a runtime dependency
// $ npm install express

// Add a dev-only dependency
// $ npm install --save-dev jest

// Run a script defined in package.json
// $ npm run start

const express = require('express');
const app = express();
app.get('/', (req, res) => res.send('Hello'));
app.listen(3000);

Follow-up Questions

• What is the difference between dependencies and devDependencies?
• What does package-lock.json do and should you commit it?
• What is the difference between npm and npx?
• How does semantic versioning (^ vs ~) affect updates?
• What is the difference between npm install and npm ci?