Let's Write a Redux Controller for Web Components

Elliott Marquez challenged me to write a redux controller on the Lit & Friends slack.

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ElliottFollow

I work on Developer experiences at Chrome and closely with the web platform

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 controllerscd controllersgit initnpm init --yesnpm i -D typescript littouch 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