Express provides a handy method to transfer a file as attachment: Response.download().

Once a user hits a route that sends a file using this method, browsers will prompt the user for download.

The Response.download() method allows you to send a file attached to the request, and the browser instead of showing it in the page, it will save it to disk.

app.get('/', (req, res) => res.download('./file.pdf'))

In the context of an app:

const express = require('express')
const app = express()

app.get('/', (req, res) => res.download('./file.pdf'))
app.listen(3000, () => console.log('Server ready'))

You can set the file to be sent with a custom filename:

res.download('./file.pdf', 'user-facing-filename.pdf')

This method provides a callback function which you can use to execute code once the file has been sent:

res.download('./file.pdf', 'user-facing-filename.pdf', (err) => {
  if (err) {
    //handle error
    return
  } else {
    //do something
  }
})

Lessons in this unit:

0:	Introduction
1:	Introduction to Express
2:	Request parameters
3:	Send a response to the client
4:	Send a JSON response
5:	Manage cookies
6:	Work with HTTP headers
7:	Handling redirects
8:	Routing
9:	Template engines
10:	Middleware
11:	Serving Static Assets with Express
12:	▶︎ Send files to the client
13:	Sessions
14:	Validating and sanitizing input
15:	Handling form data
16:	Handling CORS
17:	HTTPS with a self-signed certificate
18:	HTTPS with Let's Encrypt
19:	Handling file uploads
20:	Build a REST API with MongoDB