Hi, I am Bruno Paulino.
Software is my craft.

Modern Webapps with React, Phoenix, Elixir and TypeScript

January 19, 2022

I’ve started working on a side project this year and the tech stack I have chosen was the Elixir lang due to its functional design and fault tolerance (Thanks to the Erlang VM) so the Phoenix framework was a natural choice for me.

While Phoenix provides a very interesting programming model called LiveView, I wanted to stick with the frontend stack I’m most familiar with which is React. Besides using it heavily in my day job, I also really appreciate the ecosystem around it.

If you are a savvy Elixir engineer and just want to see the code, here is the Github repo ready for you. Feel free to leave a Github star so folks can find this template more easily.

I wanted to come up with a solid Phoenix project where I can get all the benefits from Elixir and Phoenix itself, but also be flexible enough by not coupling my React frontend with Phoenix. My requirements were:

  • Be able to use Hot Module Replacement during frontend development.
  • Run the React frontend in a separate process from the Phoenix app
  • During development, changes on the React frontend do not trigger the elixir compiler
  • During development, changes on the Phoenix app do not trigger frontend recompilation
  • CORS. I don’t want to think about it. It’s a no-brainer if we bundle all our apps together under the same domain.
  • In production, serve the React frontend under the /app/* path from Phoenix
  • In production, all other routes should be server-rendered, so we can still benefit from serve-side rendering for specific cases like better SEO and dynamic landing pages with a smart caching strategy via Cloudflare using stale-while-revalidate headers.

With the clear requirements defined above, I managed to make them all work by combining Phoenix and Vite. So let’s get our hands dirty, write some code and make this project work!

This guide assumes that you are already familiar with Elixir, Phoenix and a frontend framework like React, so we skip a few basic concepts and jump straight in. Although, I will be linking some important resources to guide you in case you are just starting with this stack.

Creating our Phoenix project

First of, make sure you have the following dependencies installed:

  1. Elixir: installation guide here
  2. Phoenix: installation guide here
  3. NodeJS 16 or above: installation guide here using NVM
  4. PostgreSQL: Download here

Now let’s head to our terminal and create our Phoenix app:

mix phx.new phoenix_react

Once your project is react, cd into it and fire up the Phoenix server:

cd phoenix_react
# Make sure the Postgres database is available for Ecto
mix ecto.create
# Start the dev server
mix phx.server

Now you should be able to access your Phoenix app at localhost:4000 and see a page like the following:

Phoenix App

Awesome! We have got our Phoenix app up and running. Let’s bootstrap our React app in an independent directory.

Creating our React with TypeScript project

For our React frontend, I’ve chosen Vite to handle all the tooling for me. It has got all the sane defaults I need for a TypeScript project with React, plus it uses ESBuild which gives us blazing fast feedback during development.

To kick things off, leave the Phoenix server running and open up a new terminal window. Still within the Phoenix directory in your terminal, let’s use the Vite CLI to create our React project:

npm init vite@latest frontend -- --template react-ts

This should create our React project under the frontend directory. Let’s install all dependencies and start our Vite dev server:

cd frontend
npm install
npm run dev

Now head to your browser at localhost:3000, you should see our React app up and running!

React App

Adding routes to our React app

There is a major difference between Phoenix routes and React routes:

  • Phoenix routes are mapped to a request to the server, which results in a new template rendering which results in the whole browser to reload.
  • React routes are client-side only, which means that navigating from /app/settings to /app/profile in our React app doesn’t mean a new request to the server. It might just mount a new component instantly which might not need server data at all.

So the strategy here is to leverage React Router on our React app for any route that is under /app and whenever the client makes the first request to our app, let’s say they are visiting example.com/app for the first time, Phoenix will handle this initial request and serve the initial HTML together with our React app payload, so the React app can be mounted and take care of the routing from there.

To make sure that client-side route changes are working, let’s add a very basic routing component so we can test if our react app is working. Let’s start by installing React Router in our React app. Stop the dev server and execute the following:

npm install react-router-dom@6

Now open up your favorite text editor and edit our React app file at phoenix_react/frontend/src/App.tsx with the following components:

import { useEffect } from "react";
import { BrowserRouter, Link, Routes, Route } from "react-router-dom";

const style = { display: "flex", gap: "8px", padding: "8px" };

function App() {
   * During development we can still access the base path at `/`
   * And this hook will make sure that we land on the base `/app`
   * path which will mount our App as usual.
   * In production, Phoenix makes sure that the `/app` route is
   * always mounted within the first request.
   * */
  useEffect(() => {
    if (window.location.pathname === "/") {
  }, []);

  return (
    <BrowserRouter basename="app">
      <nav style={style}>
        <Link to="/">Home</Link>
        <Link to="/settings">Settings Page</Link>
        <br />
        <Route path="/" element={<HomePage />} />
        <Route path="settings" element={<SettingsPage />} />

function SettingsPage() {
  return (
      <h1>Settings Page</h1>
        <li>My profile</li>

function HomePage() {
  const style = { padding: "8px" };
  return (
    <div style={style}>
      <h1>React TS Home</h1>
      <p>Welcome to the homepage</p>

export default App;

Now you should be able to visit localhost:3000/app and see a screen similar to the following:

React app with routes

Try to click around the Home and Settings Page links at the top. Notice that it transitions between pages instantly. If you check your Phoenix console, you notice that no requests have been fired to your backend. So far so good.

Also notice that we now access our React app via the /app route. This is important and plays a major role when we bundle our application for production and serve it from Phoenix. We are using a small hook to check whether our app was mounted to the / path and redirect to the base path. This is only relevant for development. In production, Phoenix will make sure that the user is always in the /app when using our React app.

Serving our React frontend from Phoenix

So far, Phoenix has no clue about our React app. We need to come up with a way to tell Phoenix how to serve our React app once it’s bundled and ready to be served as a SPA. For that to work, we can do the following:

  1. Build our React app for production with Vite
  2. Copy our production build to the priv/static folder so we can use Plug.Static to serve our static assets
  3. Make Phoenix aware about the /app route so our generated index.html from Vite can be statically served, which will trigger our React resources to be loaded.

Creating a custom mix task to do the job

To manage point 1 and 2 from the previous section, we can create a custom mix task that can execute all the TypeScript bundling via NPM and coping files around to make our React app ready to be served by Phoenix.

Our custom mix task will make sure that:

  • All of our frontend dependencies are installed
  • build our frontend for production distribution
  • Move the production files to priv/static/webapp

The /priv/static/webapp path will be picked up by Phoenix later on, but make sure that you add it to your .gitignore file. We don’t want to commit our frontend production bundles.

Let’s go ahead and create lib/mix/tasks/webapp.ex with the following Elixir code:

defmodule Mix.Tasks.Webapp do
  @moduledoc """
    React frontend compilation and bundling for production.
  use Mix.Task
  require Logger
  # Path for the frontend static assets that are being served
  # from our Phoenix router when accessing /app/* for the first time
  @public_path "./priv/static/webapp"

  @shortdoc "Compile and bundle React frontend for production"
  def run(_) do
    Logger.info("📦 - Installing NPM packages")
    System.cmd("npm", ["install", "--quiet"], cd: "./frontend")

    Logger.info("⚙️  - Compiling React frontend")
    System.cmd("npm", ["run", "build"], cd: "./frontend")

    Logger.info("🚛 - Moving dist folder to Phoenix at #{@public_path}")
    # First clean up any stale files from previous builds if any
    System.cmd("rm", ["-rf", @public_path])
    System.cmd("cp", ["-R", "./frontend/dist", @public_path])

    Logger.info("⚛️  - React frontend ready.")

Using the System module, we can interact directly with our host system, so we can issue shell commands when invoking our custom mix task.

Let’s try it out. Stop your Phoenix server and execute the following command:

mix webapp

# You should see an outout similar to the following:
15:48:13.605 [info]  📦 - Installing NPM packages
15:48:15.034 [info]  ⚙️  - Compiling React frontend
15:48:19.611 [info]  🚛 - Moving dist folder to ./priv/static/webapp
15:48:19.618 [info]  ⚛️  - React frontend ready.

Our frontend is ready to be served by Phoenix now. But there is one little change we have to make to our Vite configuration so our Frontend static assets can be delivered.

Making the webapp base path discoverable

By default, Phoenix serves static content from the priv/static directory using the base route /. For instance, if we have a JPG file at priv/static/assets/picture.jpg, Phoenix will make this resource available at /assets/picture.jpg to the public.

We want that to happen, but for our web app, static resources will be under the /webapp/ path. Luckily, this is extremely simple.

Vite base path for production

Since we want to serve our Web app from priv/static/webapp, we have to make sure that during our production build, Vite should append the /webapp/ base path to all our resources. This is paramount for our app to work.

Vite provides a specific configuration entry for that. Let’s go ahead and edit our frontend/vite.config.ts file with the following:

import { defineConfig } from "vite";
import react from "@vitejs/plugin-react";

// https://vitejs.dev/config/
export default defineConfig({
  plugins: [react()],
  // using the `webapp` base path for production builds
  // So we can leverage Phoenix static assets plug to deliver
  // our React app directly from our final Elixir app,
  // Serving all files from the `priv/static/webapp` folder.
  // NOTE: Remember to move the frontend build files to the
  // `priv` folder during the application build process in CI
  // @ts-ignore
  base: process.env.NODE_ENV === "production" ? "/webapp/" : "/",

Now execute our custom mix task again from within our Phoenix project:

mix webapp

Once this is done, take a look at the priv/static/webapp/index.html contents. We should see an HTML similar to the following:

<!DOCTYPE html>
<html lang="en">
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Vite App</title>
    <link rel="modulepreload" href="/webapp/assets/vendor.6b432119.js" />
    <link rel="stylesheet" href="/webapp/assets/index.458f9883.css" />
    <div id="root"></div>

Notice that all URLs there have the /webapp/ base path prepended. That is very neat. Our Frontend is ready to be served by Phoenix.

Serving static assets via Plug

Phoenix is still unaware of our webapp static folder. We must add that to our endpoint configuration so our Plug.Static can serve it. Head to lib/phoenix_react_web/endpoint.ex at line 23. Add the webapp to the string list:

plug Plug.Static,
    at: "/",
    from: :phoenix_react,
    gzip: false,
    only: ~w(assets fonts images webapp favicon.ico robots.txt)

With that tiny change, Phoenix is now able to serve the static assets generated by Vite.

Serving the initial HTML page via Phoenix

We now have a fully functional frontend and our Phoenix backend is able to deliver its static assets like JavaScript and CSS files. But to make it really feel native to our platform, we must be able to visit example.com/app or any other route under /app and our React app must be able to mount all its components based on the given route.

For that to work, we must deliver the initial index.html that was generated by Vite whenever someone visits /app/*. We need a custom Phoenix controller. Let’s build that now.

Create a new controller at lib/phoenix_react_web/controllers/webapp_controller.ex with the following module:

defmodule PhoenixReactWeb.WebappController do
  use PhoenixReactWeb, :controller

  def index(conn, _params) do
    |> send_resp(200, render_react_app())

  # Serve the index.html file as-is and let React
  # take care of the rendering and client-side rounting.
  # Potential improvement: Cache the file contents here
  # in an ETS table so we don't read from the disk for every request.
  defp render_react_app() do
    Application.app_dir(:phoenix_react, "priv/static/webapp/index.html")
    |> File.read!()

We now have a controller that can serve our index.html file, but we need to configure a route that will hit this newly created index function. Let’s add the following scope to our Phoenix router:

scope "/app", PhoenixReactWeb do
  get "/", WebappController, :index
  get "/*path", WebappController, :index

Awesome! Let’s try this out. Make sure that your Vite dev server is stopped and start your Phoenix server with mix phx.server and go to localhost:4000/app. You should see the exact same result that we had when our Vite dev server was running!

Try to click through the header links. It should be all client-side routing. The ultimate test is to type in the url localhost:4000/app/settings, hit enter and see what happens.

Notice that the /app/settings page will be displayed as we expected. Behind the scenes, Phoenix kept delivering the index.html file and the React Router made sure that the right components were mounted. Sweet! Our Phoenix and React apps are ready to roll!

API requests and CORS

If you have been developing frontend apps that talk to an external API, I’m quite confident that you have faced a bunch of CORS issues. For those that are not familiar with, whenever you open up an app at myapp.com and that same app needs to call an API at myapi.com the browser prevents that by default.

Actually, the browser will issue an OPTIONS request to check if myapi.com allows requests coming from myapp.com to be answered. This is a very interesting security mechanism and I’m glad it’s there. If you want to learn more about it, Jake Archibald wrote an awesome blogpost about it with all the information you need to know.

Skipping the whole CORS trouble

Whenever we are developing an app that it’s all hosted under the same domain, things are way easier and simpler. If our myapp.com makes a request to myapp.com/api/users the browser won’t even think about checking that because it knows that myapp.com is under the same domain, so it’s pretty sure that you allow requests to come and go from your own domain.

During development, we are running our Phoenix app at port 4000 and our React app at port 3000, we need to find a way for requests made by our React app to localhost:3000/api/users to be captured by some sort of proxy and forwarded to our Phoenix backend at port 4000.

Luckily, Vite saves the day again by providing us with the server proxy configuration. Head over to the frontend/vite.config.ts and add the server entry to your config:

import { defineConfig } from "vite";
import react from "@vitejs/plugin-react";

// https://vitejs.dev/config/
export default defineConfig({
  plugins: [react()],
  // Forward all requests made by our React frontend to `localhost:3000/api`
  // to our Phoenix backend running at `localhost:4000`.
  // This is only necessary during development.
  // In production, our Phoenix and React apps are served from the same
  // domain and port, which makes this configuration unecessary.
  server: {
    proxy: {
      "/api": {
        target: "http://localhost:4000",
        secure: false,
        ws: true,
  // using the `webapp` base path for production builds
  // So we can leverage Phoenix static assets plug to deliver
  // our React app directly from our final Elixir app,
  // Serving all files from the `priv/static/webapp` folder.
  // NOTE: Remember to move the frontend build files to the
  // `priv` folder during the application build process in CI
  // @ts-ignore
  base: process.env.NODE_ENV === "production" ? "/webapp/" : "/",

From now on, if you are making requests with axios for instance, you can safely make a request in your React component like this:

import { useState, useEffect } from "react";
import axios from "axios";

export function RequestComponent() {
  const [todos, setTodos] = useState([]);

  useEffect(() => {
    axios.get("/api/todos").then((response) => {
      const { todos } = response.data;
  }, []);

  return (
      {todos.map((t) => (
        <span key={t.id}>{t.content}</span>

The request to /api/todos should be forwarded to your Phoenix backend and as long as you have a route and a controller to respond to that, API requests will be served just fine.

Authentication via http-only Cookies will also just work without any extra setup since everything is under the same domain. (localhost during development and myapp.com in production)

Creating an Elixir Release

We have got everything setup now and the cherry on top is to generate the Elixir release with our production Phoenix app.

The major advantage of an Elixir Release is that it creates a single package including the Erlang VM, Elixir and all of your code and dependencies. The generated package can be placed into any machine without any preconfigured dependency. It works similarly like Go binaries that you just download and execute.

But before we generate our release, since we are testing the build locally, we need to change the port configuration since our runtime configuration is binding to 443 by default. Let’s quickly change that at config/runtime.exs:

config :phoenix_react, PhoenixReactWeb.Endpoint,
  # here use the `port` variable so we can control that with environment variables
  url: [host: host, port: port],
  # Enable the web server
  server: true,
  http: [
    ip: {0, 0, 0, 0, 0, 0, 0, 0},
    port: port
  secret_key_base: secret_key_base

With that out of the way, execute the following commands to generate the release:

# Generate a secret for our Phoenix app
mix phx.gen.secret
# It will output a very long string. Something like this:

# Now export this secret as a environment variable:
export SECRET_KEY_BASE=B41pUFgfTJeEUpt+6TwSkbrxlAb9uibgIemaYbm1Oq+XdZ3Q96LcaW9sarbGfMhy

# Export the database URL
# Probably very different in production for you.
# I'm just using the local postgreSQL dev instance for this demo
export DATABASE_URL=ecto://postgres:postgres@localhost/phoenix_react_dev

# Get production dependencies
mix deps.get --only prod

# Compile the project for production
MIX_ENV=prod mix compile

# Generate static assets in case you
# are using Phoenix default assets pipelines
# For serve-side rendered pages
MIX_ENV=prod mix assets.deploy

# Generate our React frontend using
# our custom mix task
mix webapp

# Genereate the convenience scripts to assist
# Phoenix applicaiton deployments like running ecto migrations
mix phx.gen.release

# Now we are ready to generate the Elixir Release
MIX_ENV=prod mix release

We now have our production release ready. Let’s fire it up with the following command:

PHX_HOST=localhost _build/prod/rel/phoenix_react/bin/phoenix_react start

# You should an output similar to the following
19:52:53.813 [info] Running PhoenixReactWeb.Endpoint with cowboy 2.9.0 at :::4000 (http)
19:52:53.814 [info] Access PhoenixReactWeb.Endpoint at http://localhost:4000

Great! Now our Phoenix app is running in production mode. Now head to your browser and open localhost:4000/app. You should see our React app being rendered!

We have finally succeeded with our Phoenix + React + TypeScript setup. It provides us with a great developer experience while simplifying our production builds by bundling our Phoenix app together with our React app.

Wrapping up

While that might have been a tiny bit complex to setup, I believe it is still worth it to keep your SPA decoupled from your backend. Here is a list with a few bonus point of this setup:

  • A single repo to work with which simplifies development, specially with a bigger team
  • Simpler CI/CD pipelines on the same repository
  • Free to swap out Vite in the future in case we decide to go with a different build tool
  • In the extreme case of changing our backend from Phoenix to something else, our React frontend is still fully independent and can basically be copy-pasted into a new setup.

I personally believe that the development and deployment of our applications should be simple and while having React as a dependency does increase complexity into our app, the trade-off of building web apps with it pays off in my case. Although, if you have simple CRUD apps, sticking with vanilla Phoenix templates and LiveView might be more than enough.

You can find the repo with all the changes we made on this post here.