@platform/state v0.7.55

A small, simple rx/observable based state-machine.
For applying to UI see the react bindings at @platform/state.react

Install

yarn add @platform/state

To work abstractly with a state library use the isolated type library:

yarn add @platform/state.types

Getting Started

Define your model and mutation events:

type IMyModel = {
  count: number;
};

type MyEvent = IIncrementEvent | IDecrementEvent;
type IIncrementEvent = { type: 'TEST/increment'; payload: { by: number } };
type IDecrementEvent = { type: 'TEST/decrement'; payload: { by: number } };
type IStatustEvent = { type: 'TEST/status'; payload: { status: string } };

Create a new state-machine:

import { Store } from '@platform/state';

const initial: IMyModel = { count: 0, status: string };
const store = Store.create<IMyModel, MyEvent>({ initial });

Define a listener that mutates the state based on a specific event type (equivalent to a "reducer"):

store.on<ITestIncrementEvent>('TEST/increment').subscribe((e) => {
  const count = e.state.count + e.payload.by;
  const next = { ...e.state, count };
  e.change(next); // UPDATE: New copy of state applied.
});

alternatively you can use "mutation like" syntax by passing a change function:

store
  .on<ITestIncrementEvent>('TEST/increment')
  .subscribe(e => {
    e.change(draft => {
      draft.count += e.payload.by; // UPDATE: New "structurally shared" immutable changes applied.
    }));
  });

This safely modifies an immutable clone of the state using "structural sharing" for efficiency (via immer).

Dispatch events to change state:

store.state; // => count === 0
store.dispatch({ type: 'TEST/increment', payload: { by: 1 } });
store.state; // => count === 1

Listen for changes to the state and react accordingly, for instance updating UI that may be rendering the state.:

store.changed$.subscribe((e) => {
  // ...
});

Add logic that reacts to events asynchronously and dispatches new update events (equivalent to an "epic"):

store
  .on<IIncrementEvent>('TEST/increment')
  .pipe(debounceTime(300))
  .subscribe(async (e) => {
    const status = await getNetworkStatus();
    e.dispatch({ type: 'TEST/status', payload: { status } });
  });