stateful.js

var EventEmitter = require("events").EventEmitter;

// A thing to manage/track state changes
// Changes passed to setState are queued up and effectuated in the next event loop tick
class Stateful extends EventEmitter {

  constructor() {
    this.state = this.getInitialState();
    this._stateChangeQueue = [];
    this._stateChangeInProgress = false;
  }

  getInitialState() {
    return {};
  }

  getState() {
    return this.state;
  }

  setState(change) {
    this._stateChangeQueue.push(change);

    if (!this._stateChangeInProgress) {
      setTimeout(this._flushQueue.bind(this), 0);
    }
    this._stateChangeInProgress = true;
  }
  _flushQueue() {
    var mergedChange = this._stateChangeQueue.reduce((result, change)=> Object.assign(change, result), {});
    this.state = Object.assign(this.state, mergedChange);
    this._stateChangeQueue = [];
    this.emit('change');
  }
}

module.exports = Stateful;