Post01-SubscriptionsResolvers

import { withFilter } from 'graphql-subscriptions';

...

Subscription: {
  watchDevice: {
    resolve: (payload) => payload,
    subscribe: withFilter(
      () => pubsub.asyncIterator(deviceConstants.UPDATE_DEVICE),
      (payload, args) => payload._id.toString() === args.id,
    ),
  },
  watchDevices: {
    resolve: (payload) => payload,
    subscribe: () => pubsub.asyncIterator([deviceConstants.UPDATE_DEVICE, deviceConstants.CREATE_DEVICE]),
  },
}