Build a QR code generator
In this tutorial, you will build and publish a Worker application that generates QR codes.
If you would like to review the code for this tutorial, the final version of the codebase is available on GitHub ↗. You can take the code provided in the example repository, customize it, and deploy it for use in your own projects.
Before you start
All of the tutorials assume you have already completed the Get started guide, which gets you set up with a Cloudflare Workers account, C3 ↗, and Wrangler.
1. Create a new Workers project
First, use the create-cloudflare
CLI to create a new Cloudflare Workers project. To do this, open a terminal window and run the following command:
For setup, select the following options:
- For What would you like to start with?, choose
Hello World example
. - For Which template would you like to use?, choose
Hello World Worker
. - For Which language do you want to use?, choose
JavaScript
. - For Do you want to use git for version control?, choose
Yes
. - For Do you want to deploy your application?, choose
No
(we will be making some changes before deploying).
Then, move into your newly created directory:
Inside of your new qr-code-generator
Worker project directory, index.js
represents the entry point to your Cloudflare Workers application.
All Cloudflare Workers applications start by listening for fetch
events, which are triggered when a client makes a request to a Workers route. After a request is received by the Worker, the response your application constructs will be returned to the user. This tutorial will guide you through understanding how the request/response pattern works and how you can use it to build fully featured applications.
In your default index.js
file, you can see that request/response pattern in action. The fetch
constructs a new Response
with the body text 'Hello Worker!'
.
When a Worker receives a fetch
event, the Worker returns the newly constructed response to the client. Your Worker will serve new responses directly from Cloudflare’s global network ↗ instead of continuing to your origin server. A standard server would accept requests and return responses. Cloudflare Workers allows you to respond quickly by constructing responses directly on the Cloudflare global network.
2. Handle Incoming Request
Any project you publish to Cloudflare Workers can make use of modern JavaScript tooling like ES modules, npm
packages, and async
/await
↗ functions to build your application. In addition to writing Workers, you can use Workers to build full applications using the same tooling and process as in this tutorial.
The QR code generator you will build in this tutorial will be a Worker that runs on a single route and receives requests. Each request will contain a text message (a URL, for example), which the function will encode into a QR code. The function will then respond with the QR code in PNG image format.
At this point in the tutorial, your Worker function can receive requests and return a simple response with the text "Hello Worker!"
. To handle data coming into your Worker, check if the incoming request is a POST
request:
Currently, if an incoming request is not a POST
, the function will return undefined
. However, a Worker always needs to return a Response
. Since the function should only accept incoming POST
requests, return a new Response
with a 405
status code ↗ if the incoming request is not a POST
:
You have established the basic flow of the request. You will now set up a response to incoming valid requests. If a POST
request comes in, the function should generate a QR code. To start, move the "Hello Worker!"
response into a new function, generateQRCode
, which will ultimately contain the bulk of your function’s logic:
With the generateQRCode
function filled out, call it within fetch
function and return its result directly to the client:
3. Build a QR code generator
All projects deployed to Cloudflare Workers support npm packages. This support makes it easy to rapidly build out functionality in your Workers. The ‘qrcode-svg’ ↗ package is a great way to take text and encode it into a QR code. In the command line, install and save ‘qrcode-svg’ to your project’s ‘package.json’:
In index.js
, import the qrcode-svg
package as the variable QRCode
. In the generateQRCode
function, parse the incoming request as JSON using request.json
, and generate a new QR code using the qrcode-svg
package. The QR code is generated as an SVG. Construct a new instance of Response
, passing in the SVG data as the body, and a Content-Type
header of image/svg+xml
. This will allow browsers to properly parse the data coming back from your Worker as an image:
4. Test in an application UI
The Worker will execute when a user sends a POST
request to a route, but it is best practice to also provide a proper interface for testing the function. At this point in the tutorial, if any request is received by your function that is not a POST
, a 405
response is returned. The new version of fetch
should return a new Response
with a static HTML document instead of the 405
error:
The landing
variable, which is a static HTML string, sets up an input
tag and a corresponding button
, which calls the generateQRCode
function. This function will make an HTTP POST
request back to your Worker, allowing you to see the corresponding QR code image returned on the page.
With the above steps complete, your Worker is ready. The full version of the code looks like this:
5. Deploy your Worker
With all the above steps complete, you have written the code for a QR code generator on Cloudflare Workers.
Wrangler has built-in support for bundling, uploading, and releasing your Cloudflare Workers application. To do this, run npx wrangler deploy
, which will build and deploy your code.
Related resources
In this tutorial, you built and deployed a Worker application for generating QR codes. If you would like to see the full source code for this application, you can find it on GitHub ↗.
If you want to get started building your own projects, review the existing list of Quickstart templates.