docs: add guide on subscriptions

[sarahxsanders]

Guide for subscriptions

[sarahxsanders]

@JoviDeCroock the prettier ci check is failing for _meta.ts but it looks correct

**DISREGARD :)

[benjie]

Absolutely excellent 🙌

[ardatan]

Besides this unmaintained library, we have an alternative package @graphql-yoga/subscriptions that uses the standard EventTarget, and it also allows you to use other event sources like Redis.

import { createPubSub } from '@graphql-yoga/subscriptions'
import { Redis } from 'ioredis'
import { createRedisEventTarget } from '@graphql-yoga/redis-event-target'
 
const publishClient = new Redis()
const subscribeClient = new Redis()
 
const eventTarget = createRedisEventTarget({
  publishClient,
  subscribeClient
})
 
const pubSub = createPubSub({ eventTarget })

And it is fully type safe compared to graphql-subscriptions;

const pubSub = createPubSub<{
  randomNumber: [randomNumber: number]
}>()
 
// Usage outside a GraphQL subscribe function
async function subscribe() {
  const eventSource = pubSub.subscribe('randomNumber')
 
  for await (const value of eventSource) {
    console.log(value)
    // dispose subscription after the first event has been published.
    eventSource.return()
  }
}
 
subscribe()
 
pubSub.publish('randomNumber', 3)