Hello World Server
Write and run your first Express server that responds to a browser request.
Syntax
app.METHOD(path, handler)Here is the classic first Express program. Save it as app.js and run it with node app.js. Then open http://localhost:3000 in your browser.
What each line does
require('express')loads the library.express()creates an application object, usually calledapp.app.get('/', handler)registers a route forGET /.app.listen(3000)starts the server on port 3000.
The handler receives two objects: req (the incoming request) and res (the response you send back).
Example
const express = require('express');
const app = express();
const port = 3000;
app.get('/', (req, res) => {
res.send('Hello World!');
});
app.listen(port, () => {
console.log(`Server running at http://localhost:${port}`);
});When to use it
- A bootcamp instructor walks students through writing a Hello World server to verify their Node.js and Express setup is working.
- A developer uses a minimal Hello World server as a health-check endpoint to confirm a new VM or container has outbound network access.
- A team starts every new microservice with a Hello World scaffold, then progressively layers in routes and middleware.
More examples
Classic Hello World server
The canonical first Express program: one route responds to GET / with plain text and logs the URL once ready.
const express = require('express');
const app = express();
app.get('/', (req, res) => {
res.send('Hello, World!');
});
app.listen(3000, () => {
console.log('Server running at http://localhost:3000');
});Port from environment variable
Reads the port from the environment so the same server code works in development and on cloud platforms like Heroku.
const express = require('express');
const app = express();
const PORT = process.env.PORT || 3000;
app.get('/', (req, res) => res.send('Hello, World!'));
app.listen(PORT, () => console.log(`Listening on port ${PORT}`));Hello World with JSON response
Returns a JSON object instead of plain text, matching the style of a real API health or welcome endpoint.
const express = require('express');
const app = express();
app.get('/', (req, res) => {
res.json({ message: 'Hello, World!', timestamp: new Date().toISOString() });
});
app.listen(3000);
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