metamask-extension/app/scripts/lib/ComposableObservableStore.js

import { ObservableStore } from '@metamask/obs-store';

/**
 * An ObservableStore that can composes a flat
 * structure of child stores based on configuration
 */
export default class ComposableObservableStore extends ObservableStore {
  /**
   * Create a new store
   *
   * @param {Object} [initState] - The initial store state
   * @param {Object} [config] - Map of internal state keys to child stores
   */
  constructor(initState, config) {
    super(initState);
    if (config) {
      this.updateStructure(config);
    }
  }

  /**
   * Composes a new internal store subscription structure
   *
   * @param {Object} [config] - Map of internal state keys to child stores
   */
  updateStructure(config) {
    this.config = config;
    this.removeAllListeners();
    for (const key of Object.keys(this.config)) {
      config[key].subscribe((state) => {
        this.updateState({ [key]: state });
      });
    }
  }

  /**
   * Merges all child store state into a single object rather than
   * returning an object keyed by child store class name
   *
   * @returns {Object} Object containing merged child store state
   */
  getFlatState() {
    if (!this.config) {
      return {};
    }
    let flatState = {};
    for (const key of Object.keys(this.config)) {
      const controller = this.config[key];
      const state = controller.getState
        ? controller.getState()
        : controller.state;
      flatState = { ...flatState, ...state };
    }
    return flatState;
  }
}