Today, more and more applications require offline capabilities. Whether it’s due to intermittent network connectivity or the need for working offline, providing a seamless offline experience is crucial. When using GraphQL as a query language for your client-server communication, implementing offline synchronization becomes a bit more challenging compared to traditional REST APIs.

In this article, we will explore how to implement offline synchronization in a JavaScript GraphQL client using Apollo Client.

What is Offline Synchronization?

Offline synchronization refers to the ability of an application to continue functioning even when there is no network connectivity. Users can still interact with the app, create or modify data, and these changes will be synchronized with the server once the network connection is restored.

Apollo Client and Offline Synchronization

Apollo Client is a powerful GraphQL client that allows you to seamlessly integrate GraphQL into your JavaScript applications. It already provides several tools and features for caching and managing remote data.

To implement offline synchronization with Apollo Client, you can make use of the Apollo Cache Persist library. This library extends Apollo Client and provides additional functionality for persisting data to local storage.

Getting Started

To get started, you need to install the necessary dependencies:

npm install apollo-boost apollo-cache-persist graphql react-apollo

Once installed, you can create your Apollo Client instance and configure the cache persistor:

import { ApolloClient } from 'apollo-boost';
import { persistCache } from 'apollo-cache-persist';
import { InMemoryCache } from 'apollo-cache-inmemory';

const cache = new InMemoryCache();

persistCache({
  cache,
  storage: window.localStorage,
});

const client = new ApolloClient({
  cache,
  // ...other Apollo Client options
});

This code sets up the Apollo Client with an in-memory cache and configures the cache persistor to store the data in the browser’s local storage.

Handling Offline Operations

To handle offline operations, you need to queue the mutations and subscriptions performed while the app is offline and replay them once the network connection is restored.

import { ApolloOfflineClient } from 'apollo-offline';
import { OfflineCache } from 'apollo-offline/Cache';
import { OfflineLink } from 'apollo-offline/Link';

const offlineLink = new OfflineLink();

const offlineCache = new OfflineCache(cache);

const offlineClient = new ApolloOfflineClient({
  link: offlineLink,
  cache: offlineCache,
  client,
});

By using the Apollo Offline library, you can create an instance of ApolloOfflineClient that extends Apollo Client and adds offline synchronization capabilities. The offlineLink handles queuing and executing operations when the app is offline, and the offlineCache stores the queued operations.

With these additions, your JavaScript GraphQL client now has offline synchronization capabilities.

Conclusion

Offline synchronization is essential for modern applications that require seamless offline functionality. By using Apollo Client and the Apollo Cache Persist library, you can easily add offline synchronization capabilities to your JavaScript GraphQL client.

Integrating offline synchronization can be complex, but with the right tools and libraries, Apollo Client makes it easier to handle offline operations and ensure data consistency across the client and server.

#graphql #javascript