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Francesco Leonardi for Potato

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Server Side Rendering React App with Deno


Two of my favourites things are React and dinosaurs.
In this article I will show how I’ve put them together to develop a server side rendering React application with Deno.

Project Setup

I will assume that we are all familiar with React and Deno. Knowing that Deno is pretty new, if you don’t know how to install it and how it works, I would highly suggest you to have a read at this great introduction before diving into this article.

Now let’s start creating the project structure and the files needed for this tutorial, I’m using Visual Studio Code but any editor will do.
Open your terminal and type:

mkdir deno-react-ssr && cd $_
code .
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This will create a new folder called deno-react-ssr and will open it with vscode.
In this folder we will need to create three files, app.tsx that will contain the code of the React component, server.tsx for the server code and deps.ts will contain all our dependencies. Think of it as our version of a package.json.
You will end up with a structure like this:

├── app.tsx
├── deps.ts
└── server.tsx
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Setting up the dependencies

In deps.ts we will have to export all the dependencies needed for this application to run.
Copy the following code and add it to your file.

// @deno-types=""
import React from '';
// @deno-types=""
import ReactDOMServer from '';
export { React, ReactDOMServer }
export { Application, Context, Router } from '';

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As you can see, in Deno you import the modules directly from a url.
I’ve decided to import React and ReactDOMServer from jspm as suggested in the documentation for third party modules but you can use any other CDN that provides the same modules.

One unusual thing that may stand out to you could be this:

// @deno-types=""

Since we are using typescript, this line of code will inform Deno of the location of the types it needs to import and will affect the import statement that follows. A more exhaustive explanation can be found in the Deno Type Hint manual.

I’ve also decided to use Oak, a middleware framework for Deno's http server that also provides a router, so I’m importing all the modules we will use in the server in addition to the Context type that typescript requires.

Create your React component

This is how our app.tsx component will look:

import { React } from "./deps.ts";

const App = () => {
  const [count, setCount] = React.useState(0);

  const garden = {
    backgroundColor: 'green',
    height: 'auto',
    fontSize: '30px',
    maxWidth: '400px',
    padding: '20px 5px',
    width: '100%'

  return (
    <div className="pure-g pure-u">
      <h2>My DenoReact App</h2>
      <button className="pure-button" onClick={() => setCount(count + 1)}>Add a 🦕 in your garden!</button>
      <p style={garden}>
      { Array(count).fill(<span>🦕</span>) }

export default App;

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As with any standard React component, we start by importing React from our deps.ts file.

Then we are going to declare our App component that uses hooks to implement a simple button counter that allows you to add as many dinosaurs as you want in your personal garden!

Setting up the Server

For the server I’m using Oak and the code in server.tsx will look like this:

import {
} from './deps.ts';

import App from "./app.tsx";

const PORT = 8008;

const app = new Application();
const jsBundle = "/main.js";

const js =
`import React from "";
 import ReactDOM from "";
 const App = ${App};
 ReactDOM.hydrate(React.createElement(App), document.getElementById('app'));`;  

const html =
      <link rel="stylesheet" href="">
      <script type="module" src="${jsBundle}"></script>
      <main id="app">${ReactDOMServer.renderToString(<App />)}</main>  

const router = new Router();
  .get('/', (context: Context) => {
    context.response.type = 'text/html';
    context.response.body = html;
  .get(jsBundle, (context: Context) => {
    context.response.type = 'application/javascript';
    context.response.body = js;


console.log(`Listening on port ${PORT}...`);

await app.listen({ port: PORT });
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As always we need to import all the dependencies we will use in our server.
We will also import our App we created earlier, as you can see the extension .tsx is required in Deno so don’t forget it!

Next step is to create our Oak server application and we’ll also need to define some routes:

  • '/' will serve our HTML page that contains the rendered app.
  • '/main.js' will serve our application code that is needed to hydrate the client side React application.

Finally we tell our application to use the route we just created and start listening on port 8008. You can notice I’m also using router.allowedMethods(), it’s a middleware that lets the client know when a route is not allowed.

Run the application

Running the SSR React application we just created is extremely simple, you just need to use the following command:

deno run --allow-net ./server.tsx
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Deno is built secure by default, that means that a Deno application will not be able to access your network, to overcome this we'll just need to use Deno's --allow-net flag.

Now the only thing missing is to open http://localhost:8008/ and enjoy your new App!


I hope you enjoyed the brief tutorial illustrated in this article and I’m looking forward to seeing what will happen next and how more complex applications can be built with this stack.

If you are still unclear about anything we’ve done or want a full reference of the code, here’s the GitHub repository.

Top comments (15)

craigmorten profile image
Craig Morten • Edited

FYI at the time this article was published, the current version of Deno is v1.1.1 and all the JSX troubles have been fixed 😉

Edit: I believe the author has now removed the out of date warning regarding v1.0.2 for anyone confused by my now seemingly random comment!

fleonard profile image
Francesco Leonardi • Edited

Thanks for the sanity check!
I've actually wrote the code and the blog post way before it was scheduled to be published and forgot to check the current release, I'll update the post accordingly 👍

craigmorten profile image
Craig Morten • Edited

Nice one!

Yeah Deno is moving incredibly fast atm, so easy to draft something and then find it's already out of date! Already the case for a v. suspiciously similar article I wrote about a month ago on the same topic (REF: - it's an effort to keep everything current 😂

Thread Thread
fleonard profile image
Francesco Leonardi

Yeah totally agree, happens every time you start trying out new tech.
I guess it's one of the fun parts of been a developer!

craigmorten profile image
Craig Morten

P.S. JSPM has also migrated it's CDN from to 😄


fleonard profile image
Francesco Leonardi • Edited

Yeah I saw that and updated the article even tho, as they state in the release, will still be available for a further 12 months until June 2021.

gurb profile image
gurb • Edited

Thanks for information. I got this error, code error: error sending request for url ( error trying to connect: dns error: No such host is known. (os error 11001). Deno 1.1.1 - Windows 10 - VsCode 1.46.1

edit: "Cannot find module '' or its corresponding type declarations.ts(2307)"

fleonard profile image
Francesco Leonardi • Edited

I'm not actually able to replicate the issue. This is the Deno version I'm running:

deno 1.1.1
v8 8.5.104
typescript 3.9.2

Have you tried by any chance to manually do :

deno upgrade --version 1.1.1

and then:

deno run --allow-net --reload  ./server.tsx

Using the --reload flag will force a reload of all the modules you have already cached.

gurb profile image

I never downloaded before react-dom. I suppose their servers broken temporarly. Thank you.

a2lop profile image
andres lopez

Hey! Nice article! Where service do you suggest to host this deno-react ssr application?

fleonard profile image
Francesco Leonardi

I think the easiest way would be to create a Docker container for the app and then you should be able to deploy to any service you want.
You can have a look at Deno Docker to check how to set it all up.

downey profile image
Tim Downey

Where does all the dinosaur artwork for Deno come from? I'm pretty unfamiliar with Deno, but I feel like things with a good mascot (e.g. Docker, Golang) often end up being successful... 😅

craigmorten profile image
Craig Morten

The original icon design was Ryan Dhal himself. A lot of the most popular banners/images in use are by the artist hashrock (including the banner of this article).

You can check out artwork and the artists on (not everything is on there, but by clicking through to artists’ GitHub you can generally find more). Be sure to give them credit!

downey profile image
Tim Downey

Thank you!

ije profile image

nice tutorial!! maybe you can try Aleph.js, a react framework in deno, like nextjs.