Hello world example

<div class="doc-box doc-info" markdown="1"> 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](/{{ page.lang }}/starter/generator.html), which creates the scaffolding for a full app with numerous JavaScript files, Jade templates, and sub-directories for various purposes. </div>

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](/{{ page.lang }}/starter/installing.html).

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

<div class="doc-box doc-notice" markdown="1"> 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. </div>

Run the app with the following command:

bash

$ node app.js

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

Express "Hello World" example

Hello world example

Running Locally