WebSocketLink.ts

import { ApolloLink, Operation, FetchResult, Observable } from 'apollo-boost';
import { print, GraphQLError } from 'graphql';
import { createClient, ClientOptions, Client } from 'graphql-ws';

// See example taken from https://github.com/enisdenjo/graphql-ws#apollo-client
class WebSocketLink extends ApolloLink {
  private client: Client;

  constructor(options: ClientOptions) {
    super();
    this.client = createClient(options);
  }

  public request(operation: Operation): Observable<FetchResult> {
    return new Observable((sink) => {
      return this.client.subscribe<FetchResult>(
        { ...operation, query: print(operation.query) },
        {
          next: sink.next.bind(sink),
          complete: sink.complete.bind(sink),
          error: (err) => {
            if (err instanceof Error) {
              return sink.error(err);
            }

            if (err instanceof CloseEvent) {
              return sink.error(
                // reason will be available on clean closes
                new Error(
                  `Socket closed with event ${err.code} ${err.reason || ''}`,
                ),
              );
            }
            
            return sink.error(
              new Error(
                (err as GraphQLError[])
                  .map(({ message }) => message)
                  .join(', '),
              ),
            );
          },
        },
      );
    });
  }
}