Serverless Deno + React with server-side rendering on Begin

Paul Chin Jr
May 14, 2020

Brown toy dinosaur Photo by Maria Oswalt on Unsplash

Deno is a next-generation JavaScript runtime that features a built-in TypeScript compiler and code bundler, allowing developers to create applications without Webpack, Babel, or Rollup. Oh, and we can run Deno in serverless functions! Combining these results in a much cleaner codebase for server-side rendered React.js applications.

In this post we’ll look at an example app deployed on Begin with CI/CD.


You can install Deno in a few different ways. I chose to install it with brew install deno, but you can check their docs for other methods.

Try out a Deno + React app right now

Hit this button to deploy a Deno React app to Begin in 30 seconds (no credit card required):


After deploying to Begin, you’ll have a new repo. Let’s clone it and take a closer look:

git clone{username}/{repo-name}.git
cd {repo-name}
npm install

File structure

Begin uses the OpenJS Architect project to help us structure our serverless applications and deploy them with infrastructure as code. The power of deterministic deployments directly to serverless backends comes from the app.arc file, so let’s open it up and take a look.

# .arc file
# your app's namespace
# the source folder of your static bundle output
folder dist
# declaration of routes, which are individual http functions
get /

You’ll also see a directory for src/http/get-index which contains all the code that gets executed from a user request to the root of your application.

What’s noticeably missing is a rollup.config.js or a tsconfig.json because Deno, the runtime, will compile and bundle the code for us. To use Deno in Begin, make sure there’s a src/http/get-index/.arc-config file that contains:

runtime deno

Begin will take care of the rest!

Inside the app

Let’s start with src/browser.tsx, this file is the entry point for our client-side JavaScript that executes once all the DOM content is loaded.

// src/browser.tsx
import { React, ReactDOM } from ''
import { App } from './http/get-index/app.tsx'
window.addEventListener('DOMContentLoaded', () => {
  let el = window.document.getElementById('app')
  ReactDOM.hydrate(<App/>, el)

Because Deno can work with ES modules, we can use the import syntax and only load parts of the package we need from an URL. That’s pretty nifty — and efficient!

Next, let’s look at the src/http/get-index/index.ts file for our serverless function.

// src/http/get-index/index.ts
import { render } from './render.tsx'
export async function handler() {
  return {
    headers: {
      'content-type': 'text/html; charset=utf8'
    body: await render()

This file will generate the final response from our app and emit an HTML string to the client.

So what’s in the src/http/get-index/render.tsx file?

import ReactDOMServer from '';
import { React } from "";
import { App } from './app.tsx';
export async function render() {
  let body = ReactDOMServer.renderToString(<App/>);
  return `<!DOCTYPE html>
  <div id=app>${body}</div>
  <script type="module" src=/_static/browser.js></script>

This is the render function that gives us server-side rendering. It takes in a component, <App/> , and wraps it in an HTML document with a <script> tag to load the client-side bundle.

Now we can get to the beating heart of our app logic!

// src/http/get-index/app.tsx
import React, { Component } from "";
declare global {
  namespace JSX {
    interface IntrinsicElements {
      p: any;
type Props = {};
type State = {
  time: Date;
export class App extends Component<Props, State> {
  state = {
    time: new Date(),
componentDidMount() {
    setInterval(() => this.tick(), 1000);
tick() {
      time: new Date(),
render() {
    return <p>The current time is {this.state.time.toLocaleTimeString()}</p>;

Our app is now a real-time clock that executes on the client to update the DOM every second with the current time.

Cheetah running Photo by Cara Fuller on Unsplash

Local development

If you’ve made it this far and wondered how to get this running locally, just run npm start from the command line. This start script will compile, bundle, and serve your app with @architect/sandbox. Sandbox is a complete development server that emulates API Gateway, Lambda functions, and much more.

Find out more about setting up Begin apps.

Set up CI/CD

You’re already done! Every Begin app builds, tests, and deploys your app to staging each time you push a commit to master. When you’re ready for production, you can hit the “Deploy to Production” button from the Begin console ( or git tag a release).

Next Steps