model.js

import {Subject} from 'rxjs';

export default class Model {
  constructor(state) {
    this.state = state;
    this.loading = false;
    this.error = null;
    this._delta = new Subject(this);
    this._subs = [];
  }

  /** Update the state of this model and publish related events */
  async _update(operation) {
    this.loading = true;
    this._delta.next(this);
    try {
      await operation();
      this.loading = false;
      this.error = null;
    }
    catch (error) {
      this.loading = false;
      this.error = error;
    }
  }

  /** Subscribe to changes on this model */
  subscribe(onChange) {
    this._delta.subscribe(onChange, async (error) => {
      await this._update(() => {
        throw error;
      });
    });
  }

  /** Dispose any pending operations */
  dispose() {
    this._subs.map(i => i.unsubscribe()());
    this._subs = [];
  }
}