Real-time communication is a crucial requirement for many modern web applications. With the rise of GraphQL as a powerful query language for APIs, it’s essential to also support real-time updates through subscriptions.

In this blog post, we will explore how to implement real-time subscriptions with GraphQL in JavaScript, using the popular Apollo Client library.

What are GraphQL Subscriptions?

GraphQL subscriptions allow clients to receive real-time updates from the server when specific data changes. Instead of sending periodic requests to fetch updated data, the server pushes updates to the client as soon as they occur.

Setting Up the Server

To get started, we need to set up a GraphQL server that supports subscriptions. We’ll use the Apollo Server library for this. Here is a simple example of setting up an Apollo Server with subscriptions enabled:

const { ApolloServer, PubSub } = require('apollo-server');
const pubsub = new PubSub();

const typeDefs = `
  type Post {
    id: ID!
    title: String!
  }

  type Query {
    posts: [Post]
  }
  
  type Mutation {
    createPost(title: String!): Post
  }
  
  type Subscription {
    newPost: Post
  }
`;

const resolvers = {
  Query: {
    posts: () => [{ id: 1, title: 'Hello world' }, { id: 2, title: 'GraphQL is awesome' }],
  },
  Mutation: {
    createPost: (_, { title }) => {
      const post = { id: Date.now().toString(), title };
      pubsub.publish('NEW_POST', { newPost: post });
      return post;
    },
  },
  Subscription: {
    newPost: {
      subscribe: () => pubsub.asyncIterator('NEW_POST'),
    },
  },
};

const server = new ApolloServer({ typeDefs, resolvers });

server.listen().then(({ url, subscriptionsUrl }) => {
  console.log(`Server ready at ${url}`);
  console.log(`Subscriptions ready at ${subscriptionsUrl}`);
});

This example sets up a simple GraphQL schema with a Post type, Query and Mutation operations, and a Subscription for new posts. The createPost mutation publishes a new post event using the pubsub functionality from Apollo Server.

Using Apollo Client for Subscriptions

On the client-side, we can use Apollo Client to subscribe to the server’s real-time updates. Here’s an example of setting up subscriptions with Apollo Client in a React application:

import React, { useEffect } from 'react';
import { useSubscription } from '@apollo/client';

import { NEW_POST_SUBSCRIPTION } from './graphql/queries';

const NewPostSubscription = () => {
  const { data } = useSubscription(NEW_POST_SUBSCRIPTION);

  useEffect(() => {
    if (data) {
      // Handle new post update
    }
  }, [data]);

  return <div></div>; // Render your React component here
};

export default NewPostSubscription;

In the code snippet above, we define a new component NewPostSubscription that uses the useSubscription hook from Apollo Client to subscribe to the NEW_POST_SUBSCRIPTION defined in the GraphQL query file. Whenever a new post event is published by the server, the component will receive the updated data through the data object.

Conclusion

Implementing real-time subscriptions with GraphQL allows web applications to deliver instant updates to clients without unnecessary polling. By using Apollo Client’s built-in subscription support, we can easily integrate real-time functionality into our JavaScript applications.

By embracing GraphQL subscriptions, developers can build highly responsive applications with real-time updates, improving the overall user experience.

#GraphQL #RealTimeSubscriptions