recording-a-navigable-history-of-the-stream-of-states.md

Recording a navigable history of the stream of states

The Aurelia Store plugin provides a powerful feature for recording and navigating through the history of state changes in your application. This can be incredibly useful for debugging, implementing undo/redo functionality, and gaining insights into how your application's state evolves over time.

To enable history tracking, you need to configure it during the plugin registration in your main.ts file:

// main.ts
import { Aurelia } from 'aurelia-framework';
import { initialState } from './state';

export function configure(aurelia: Aurelia) {
  aurelia.use
    .standardConfiguration()
    .feature('resources');

  // ... other configuration ...

  aurelia.use.plugin('aurelia-store', {
    initialState,
    history: {
      undoable: true, // Enable history tracking
    },
  });

  aurelia.start().then(() => aurelia.setRoot());
}

Explanation:

• history: { undoable: true }: This option tells the Aurelia Store plugin to start recording the history of state changes.

The StateHistory<T> Object

When history is enabled, the state property of the store (which you subscribe to) will no longer emit simple State objects. Instead, it will emit StateHistory<State> objects. The StateHistory interface looks like this:

// aurelia-store -> history.ts
export interface StateHistory<T> {
  past: T[];
  present: T;
  future: T[];
}

Explanation:

• past: T[]: An array of previous states, representing the history of state changes.
• present: T: The current state of the application.
• future: T[]: An array of states that have been undone (using the jump action, which we'll discuss later). These states can be "redone" by moving them back to the present.

Example:

// app.ts
import { inject } from 'aurelia-framework';
import { Store, StateHistory } from 'aurelia-store';
import { State } from './state'; // Import your State interface

@inject(Store)
export class App {
  private state: StateHistory<State>;

  constructor(private store: Store<StateHistory<State>>) {
      this.store.state.subscribe(
        (state: StateHistory<State>) => (this.state = state)
      );
  }
}

In this example, the state property of the App component will now hold a StateHistory<State> object, giving you access to the past, present, and future states.