Hello world example

Embedded below is essentially the simplest Express app you can create. It is a single file app — _not_ what you'd get if you use the [Express generator](/en/starter/generator), which creates the scaffolding for a full app with numerous JavaScript files, Jade templates, and sub-directories for various purposes.

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

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

app.listen(port, () => {
  console.log(`Example app listening on port ${port}`);
});

This app starts a server and listens on port 3000 for connections. The app responds with “Hello World!” for requests to the root URL (/) or route. For every other path, it will respond with a 404 Not Found.

Running Locally

First create a directory named myapp, change to it and run npm init. Then, install express as a dependency, as per the installation guide.

In the myapp directory, create a file named app.js and copy the code from the example above.

The `req` (request) and `res` (response) are the exact same objects that Node provides, so you can invoke `req.pipe()`, `req.on('data', callback)`, and anything else you would do without Express involved.

Run the app with the following command:

$ node app.js

Then, load http://localhost:3000/ in a browser to see the output.