Spotted Arrow


Less Redux Boilerplate with Union Types

If you have ever setup Redux in a new project you know the crazy amount of boilerplate that’s needed to “get started.” You need a store, reducers, selectors, actions, health insurance, and the exact date of the last time you travelled abroad. Yes, I understand the argument for “separation of concerns” and how the splitting up of files is supposed to help me reason about my application better. I think, though, this has been taken to an extreme. What about rethinking this whole split file structure and instead think of modules as a separation of data, not responsibility.

That was a bit of context and philosophy behind what spurred this blog post. Now let’s get into coding something. We are going to create a simple counter (sorry I am not original!) with the help of the union-type library with influence from The Elm Architecture.

To get started let’s pull in the necessary libraries and create a simple react application using create-react-app.

$ create-react-app redux-union && cd redux-union && yarn add union-type redux react-redux ramda && yarn start

You might want to watch this to kill the time. It’s going to be a while 😁.

After everything is installed, create a single index.js file within a store folder and pull in the necesary dependencies.

import { combineReducers, createStore } from "redux";
import Type from "union-type";
import memoize from "ramda/src/memoize";
import path from "ramda/src/path";

Okay, so what is a union type? A union type is a common data structure in functional programming languages. Essentially, it allows you to extend data types all under a single parent. For example, in Elm you will commonly see the typeMsg. Then underneath Msg there will be ButtonClick in this format: type Msg = ButtonClick | NoOp. This allows you to then pattern match in your update function on a Msg whenever one is sent from a handler in the DOM.

case msg of
  ButtonClick ->
      model ! []

It’s a really nice pattern that simplifies a common process: handling user interaction. It also allows you to be more declarative with your program by creating data types on the fly that speak more to the domain specific terminology of your application. Let’s now create the messages for this program.

const Msg = Type({ INCREMENT: [], DECREMENT: [] });

I am keeping with some Elm conventions here. Instead of calling these Actions for example, I simply call them Msg, short for message. I think this makes more sense for not just a beginner, but anyone with any background not in JavaScript or Elm. The [] is essentially the types that would be passed to these type unions if we passed any types. For example, a number. In this case we are not passing anything so it’s left empty. Now that I have my types let’s create the handlers for these different messages.

const nextState = Msg.caseOn({
  INCREMENT: (state) => ({ count: state.count + 1 }),
  DECREMENT: (state) => ({ count: state.count - 1 }),
  _: (state) => state,

There is one thing that is a bit obscure about this function. In the background you are passing action and state to nextState. So to visually understand just imagine nextState as nextState(action, state).

In the typical Elm way, let’s describe the model, in this case the state.

const initialState = {
  count: 0,

Next, let’s create the update function, in this case the reducer which will be called state.

function state(state = initialState, { type = Msg.DEFAULT, payload = null }) {
  if (typeof type === "string") return state;
  return nextState(type, state);

I had a couple issues with getting the application to initialize properly with Redux but if (typeof type === "string") return state seemed to do the trick. Usually the first action to a reducer is @@redux/INIT to initialize it. It seems other actions were being passed as well that were also strings, so to get around this I just did a catch all for those actions coming from Redux.

Next, it’s time to initialize the store.


const store = createStore(

If you have the redux-devtools-extension, then great! But don’t worry about it. We have a store, with a key of state, that also has a state key on it. Here I just want to work with a single reducer, not multiple. KISS! 💋

With the store initialized I can create actions to dispatch to the store.

export const add = () => store.dispatch({ type: Msg.INCREMENT });
export const subtract = () => store.dispatch({ type: Msg.DECREMENT });

Friendly Tip: You will find that when you fire an action, in the redux-devtools you will see [object Object] instead of the actual action. You might want to configure your own logger to correctly log out the actions.

One reason I like this is because I don’t have to pass mapDispatchToProps to my connect function. I am trying to create less boilerplate, not more!

Next to last, create a selector for your state. Here I am using some helpers from Ramda to create a memoized selector.

export const count = memoize(path(["state", "count"]));

Last but not least, let’s export the store in order to pass it down as a prop to our component.

export default store;

That wasn’t too bad was it? At this point you can now wrap your application with Provider and your App component with connect passing in mapStateToProps.

Inside of App.js this is what I have.

import React from "react";
import { add, subtract, count } from "./store";
import { connect } from "react-redux";

const mapStateToProps = (state) => ({ count: count(state) });

export default connect(mapStateToProps)(({ count }) => {
  return (
    <div className="App">
      <button type="button" onClick={add}>
      <button type="button" onClick={subtract}>

Remember to update your index.js file with the Provider.

import React from "react";
import ReactDOM from "react-dom";
import { Provider } from "react-redux";
import "./index.css";
import App from "./App";
import registerServiceWorker from "./registerServiceWorker";

import store from "./store";

  <Provider store={store}>
    <App />

In this lesson you learned about union types and how to use them to reduce your Redux boilerplate. This also implies adhering to some conventions around file structure. This is not perfect and I am sure there are even more ways to make your Redux footprint smaller. If there is, please share! I am interested to hear how this model can be improved. Thank you and until next time, keep hacking!

Did you know you can add additional type security in your application with union types? It’s not something I talked very much about here but something that I think is worth your time looking into.

The repo for this article can be found 👇

For an async example, ✔️ this one out ↓

This article was influenced by Josh Burgess demo on a similar topic:

This article has Webmentions