Express.js — Installation Guide

Step 1: Create a project

bash

mkdir my-express-app
cd my-express-app
npm init -y

npm init -y creates a package.json with default values, skipping the interactive prompts — fine for learning, worth answering properly (name, description, entry point) for a real project.

Step 2: Install Express

bash

npm install express

This adds express to dependencies in package.json and installs it into node_modules. Check package.json afterward — you should see something like "express": "^4.19.2" (or ^5.x depending on what's current when you install).

Step 3: A minimal "Hello World" server

Create server.js:

javascript

const express = require('express');
const app = express();
const PORT = 3000;

app.get('/', (req, res) => {
  res.send('Hello World!');
});

app.listen(PORT, () => {
  console.log(`Server listening on http://localhost:${PORT}`);
});

If your package.json has "type": "module", use ES module syntax instead:

javascript

import express from 'express';
const app = express();
const PORT = 3000;

app.get('/', (req, res) => {
  res.send('Hello World!');
});

app.listen(PORT, () => {
  console.log(`Server listening on http://localhost:${PORT}`);
});

Step 4: Run it

bash

node server.js

Open http://localhost:3000 in a browser or run curl http://localhost:3000 — you should see Hello World!.

Step 5: Auto-restart during development

Restarting node server.js manually after every code change gets old fast. Two real options:

Option A — Node's built-in --watch flag (no extra dependency, available in modern Node versions):

bash

node --watch server.js

Option B — nodemon (the long-standing, widely-used community tool, still common in existing tutorials and codebases):

bash

npm install --save-dev nodemon
npx nodemon server.js

Add it as an npm script in package.json for convenience:

json

{
  "scripts": {
    "dev": "node --watch server.js"
  }
}

Then just run npm run dev. (needs verification — confirm whether --watch is stable/recommended over nodemon in the specific Node version actually in use, since this has shifted as --watch matured)

Next Steps

Express is installed and a server is running. Go to Fundamentals to learn routing, the request/response objects, and middleware — the concepts everything else in Express builds on.