code: function(callback) {
      if (typeof callback === 'function') {
        this.afterSync(callback);
      }
  
      if (this.pendingSync) {
        return false;
      }
  
      var fallback = setTimeout(this.syncNow, 500);
      this.windows = this.windows.filter(this.removeClosed);
      this.pendingSync = this.windows.map(this.queueSync).concat(fallback);
      return true;
    }
docs: Schedules an observer sync cycle which checks all the observers to see if they've changed.