Implementing Real-time Data Fetching in React.js and GraphQL: Best Practices and Performance Optimization Techniques
Published: 2023-05-22 14:28:47

Real-time data fetching has become an essential feature in modern web applications. Users now expect to see up-to-date information without refreshing their browsers. Technologies like React.js and GraphQL can help meet these requirements more efficiently. This article discusses the benefits of using GraphQL alongside React.js to build real-time data fetching capabilities in web applications, covering best practices and performance optimization techniques with practical examples.

## The Power of GraphQL and React.js
React.js, a powerful JavaScript library for building user interfaces, coupled with GraphQL, a query language for APIs, offers robust capabilities for fetching data in real time. GraphQL provides a more efficient data fetching mechanism than traditional REST APIs. It reduces over-fetching and under-fetching issues by allowing clients to specify exactly what data they need.

On the other hand, React.js makes UI development a breeze. Its component-based structure promotes reusability and maintainability. But how can we benefit from both technologies for real-time data fetching? Let's dive in!

## GraphQL Subscriptions for Real-time Data
GraphQL Subscriptions are a GraphQL feature enabling real-time notifications from the server to the client. They use the pub/sub (publish–subscribe) model, which fits nicely into the GraphQL architecture.

Let's consider an example of a chat application. We will use apollo-client for managing GraphQL in our React application:

First, install Apollo Client and its utilities:


`npm install @apollo/client graphql subscriptions-transport-ws`
Let's define a GraphQL subscription for new messages:


```
subscription NewMessage {
  newMessage {
    id
    text
    user {
      name
    }
  }
}
```
This subscription informs the server that the client wants to be notified whenever a new message is posted.

In React, we can use the useSubscription hook from Apollo Client to subscribe to new messages:



```
import { useSubscription, gql } from '@apollo/client';

const NEW_MESSAGE_SUBSCRIPTION = gql`
  subscription NewMessage {
    newMessage {
      id
      text
      user {
        name
      }
    }
  }
`;


function Messages() {
  const { data, loading, error } = useSubscription(NEW_MESSAGE_SUBSCRIPTION);

  if (loading) return <p>Loading...</p>;
  if (error) return <p>Error :(</p>;

  return <p>New message from {data.newMessage.user.name}: {data.newMessage.text}</p>;
}
```
The useSubscription hook takes care of everything, such as setting up the subscription, handling incoming data, and cleaning up when the component unmounts. With this in place, our Messages component updates in real-time whenever a new message arrives.

## Performance Optimization Techniques

While GraphQL and React offer significant advantages, it's essential to consider optimization techniques to ensure your application performs smoothly.

**1. Use Fragments for Shared Fields**
In GraphQL, fragments are a collection of fields that can be reused in multiple queries, mutations, or subscriptions. By using fragments, you avoid unnecessary duplication and improve your app's performance:


```
fragment UserData on User {
  id
  name
}

subscription NewMessage {
  newMessage {
    id
    text
    user {
      ...UserData
    }
  }
}
```
**2. Use shouldComponentUpdate in React**
React's shouldComponentUpdate lifecycle method can be used to prevent unnecessary re-renders, improving the performance of your React components. By default, React re-renders components on every state change, even when the render output is the same. With shouldComponentUpdate, you can manually determine whether a re-render is needed:


```
class Messages extends React.Component {
  shouldComponentUpdate(nextProps, nextState) {
    return this.props.messages !== nextProps.messages;
  }

  render() {
    // render logic
  }
}
```
In this example, Messages will only re-render when the messages prop changes.

**3. Use React.memo**
React.memo is a higher order component that memorizes the rendered output of your functional components and only re-renders them when their props change:


```
const Messages = React.memo(function Messages({ messages }) {
  // render logic
});
```
Similar to the shouldComponentUpdate example, Messages will only re-render when the messages prop changes.

**Conclusion**
Using GraphQL alongside React.js provides an efficient and streamlined process to implement real-time data fetching in your web applications. However, don't forget to implement performance optimization techniques like using GraphQL fragments and avoiding unnecessary re-renders in React. By doing so, you'll ensure your app delivers real-time updates to users efficiently while maintaining top-notch performance. Happy coding!