### Install Express.js

Source: https://expressjs.com

Use npm to install Express.js. This command saves Express as a dependency in your project's package.json file.

```bash
$ npm install express --save
```

--------------------------------

### Hello World Express App

Source: https://expressjs.com

A basic Express application that listens on port 3000 and responds with 'Hello World!' to requests on the root path. Ensure Node.js is installed to run this code.

```javascript
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}`)
})
```

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