Subscription

If a client wants to get notified of certain changes then a subscription is the way to go. In the background Web Sockets are used to push the update from the server to the client. This is a better alternative then for example polling, which is also easily doable with Apollo.

Subscription

With GraphQL Yoga we can use GraphQL Subscriptions to implement this functionality. First we import PubSub and add it to our context property of our server.

import { PubSub } from 'graphql-yoga';

const pubSub = new PubSub();

Then we need to define the schema, here we define a count method that will increment a counter every second:

type Subscription {
  count: Int!
}

Last we need to define the resolver:

const resolvers = {
  Subscription: {
    count: {
      subscribe(parent, args, { pubSub }) {
        let counter = 0;
        setInterval(() => { 
          counter++;
          pubSub.publish('count', { // this call could be anywhere in our application, it just happened to be here
            count: counter  // property must have same name as the channel
          })
        }, 1000);
        return pubSub.asyncIterator('count'); // count is the name of the channel
      }
    }
  }
}