Let's Write a Redux Controller for Web Components

Elliott Marquez challenged me to write a redux controller in the Lit community.

So let's get cracking!

Step 0: The Setup

First step let's make a new project and import some dependencies to help us develop.

mkdir controllers
cd controllers
git init
npm init --yes
npm i -D typescript lit
touch reducer.ts

Ok next we'll set up the controller class in reducer.ts

import type { ReactiveController, ReactiveControllerHost } from 'lit';

export class ReducerController implements ReactiveController {
  constructor(
    public host: ReactiveControllerHost,
  ) {
    host.addController(this);
  }

  hostUpdate()?: void;
}

That hostUpdate signature is just to keep typescript from complaining. 🤷.

Step 1: Reducers

Our controller essentially bolts some statefullness onto a function which takes some state T and some action A and returns some other or the same state T. So let's formalize that:

type Reducer<T, A> = (state: T, action: A) => T;

The controller should take that reducer, along with some initial state, and pin them to the class instance.

export class ReducerController<T = unknown, A = unknown> implements ReactiveController {
  public state: T;

  constructor(
    private host: ReactiveControllerHost,
    public reducer: Reducer<T, A>,
    public initialState: T,
  ) {
    this.host.addController(this);
    this.state = initialState;
  }

  hostUpdate?():void
}

Step 2: Actions

Believe it or not we're pretty much done. The last piece we need is to implement a dispatch method which takes an action A and updates the host.

dispatch(action: A): void {
  this.state = this.reducer(this.state, action);
  this.host.requestUpdate();
}

And, as Chef John would say, that's it!

If we want to use our controller, we just create it on a compatible host (like LitElement) and we're off to the races:

Live Demo