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)
    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 in config) {
      if (Object.prototype.hasOwnProperty.call(config, key)) {
        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() {
    let flatState = {}
    for (const key in this.config) {
      if (Object.prototype.hasOwnProperty.call(this.config, key)) {
        const controller = this.config[key]
        const state = controller.getState
          ? controller.getState()
          : controller.state
        flatState = { ...flatState, ...state }
      }
    }
    return flatState
  }
}