Simple Angular Service example with GraphQL Queries, Mutations and Subscriptions using Apollo Client for Angular

app.service.ts

import { Injectable } from '@angular/core';
import { Apollo } from 'apollo-angular';

import {
  QUERY_USERS,
  MUTATION_LOGIN,
  SUBSCRIPTION_POST
} from './graphql';

@Injectable({
  providedIn: 'root'
})
export class AppService {
  constructor(
    private apollo: Apollo,
  ) { }

  login(email: string, password: string) {
    return this.apollo.mutate({
      mutation: MUTATION_LOGIN,
      variables: {
        email,
        password
      }
    }).toPromise(); // returning as promise
  }

  users() {
    return this.apollo.query({
      query: QUERY_USERS
    }).toPromise();
  }

  posts() {
    return this.apollo.subscribe({
      query: SUBSCRIPTION_POST
    }); // return subscription
  }
}