Loading UI and Suspense Boundaries in App Router

Table of Contents

1. Introduction
2. What is Suspense in React?
3. App Router and Suspense Boundaries in Next.js
4. How to Implement Suspense Boundaries in Next.js
5. Creating a Loading UI with Suspense
6. Handling Async Data Fetching with Suspense
7. Optimizing User Experience with Loading States
8. Best Practices for Loading UIs and Suspense Boundaries
9. Conclusion

1. Introduction

Handling asynchronous operations like data fetching, dynamic imports, or external API calls is a key part of modern web development. In React, the Suspense API provides an elegant way to manage these asynchronous tasks by allowing you to display a loading state while waiting for the content to be fetched or loaded. In the context of Next.js, specifically with the App Router, Suspense helps in improving the user experience by handling loading states gracefully.

In this module, we’ll dive into how you can leverage Suspense boundaries and loading UI with App Router to create smoother, more dynamic web applications. We will explore how Suspense works, its integration with Next.js’s App Router, and how you can implement a loading UI that improves your app’s performance and user experience.

2. What is Suspense in React?

Suspense is a feature in React that allows you to delay rendering a part of your component tree until some asynchronous operation (like data fetching or lazy loading a component) has completed. It provides a way to display fallback UI (e.g., a loading spinner) while the asynchronous task is in progress.

Before Suspense, developers had to manually manage loading states with state variables and conditionally render UI. Suspense makes this process easier and declarative, allowing the framework to handle it behind the scenes.

Key Features of Suspense:

• Fallback UI: Suspense allows you to specify a fallback UI that can be shown until the async operation finishes.
• Async Data Fetching: Suspense integrates smoothly with libraries like React Query, Relay, and GraphQL, allowing you to wait for the async operation to finish before rendering the component.
• Code Splitting: With React.lazy and Suspense, you can load components only when they are needed (lazy loading), reducing the initial load time.

3. App Router and Suspense Boundaries in Next.js

In Next.js 13+, the App Router provides a new way to organize routes and layout-based navigation in your application. One of its key features is the integration with Suspense boundaries, which allows you to handle async operations like data fetching more efficiently.

Suspense boundaries are essentially a boundary within your component tree that tells React to wait for certain data or components to load before rendering the children inside the boundary.

The App Router’s integration with Suspense lets you set loading UI at the route level or even at the layout level, improving the performance of your app by optimizing how it handles loading states.

4. How to Implement Suspense Boundaries in Next.js

Next.js supports Suspense boundaries in both pages and layouts, but you need to enable it through the App Router. Let’s look at the steps to implement Suspense boundaries and loading UI in a Next.js application.

Step 1: Enable Suspense in App Router

First, ensure that your Next.js version supports the App Router. You can enable Suspense for specific routes or layouts by wrapping them in a Suspense component.

tsxCopyEdit// In a layout or page file
import { Suspense } from 'react';

export default function PageLayout({ children }) {
  return (
    <Suspense fallback={<div>Loading...</div>}>
      {children}
    </Suspense>
  );
}

Here, we’ve added a Suspense boundary that wraps around the page’s content. The fallback UI (<div>Loading...</div>) will be shown until the content is ready to be rendered.

Step 2: Use Suspense with Async Data Fetching

Next.js works seamlessly with Suspense when handling data fetching with functions like getServerSideProps, getStaticProps, or `React’s Suspense-enabled data fetching solutions. The App Router supports data fetching at the layout level or page level with Suspense.

For instance, to fetch data inside a Suspense boundary:

tsxCopyEditimport { Suspense } from 'react';

async function fetchData() {
  const res = await fetch('https://api.example.com/data');
  return res.json();
}

export default function Page() {
  const data = fetchData();

  return (
    <Suspense fallback={<div>Loading Data...</div>}>
      <div>{JSON.stringify(data)}</div>
    </Suspense>
  );
}

The Suspense component will show the loading UI until fetchData completes and the data is available for rendering.

5. Creating a Loading UI with Suspense

Creating an effective loading UI is key to maintaining a smooth user experience during asynchronous operations. A loading UI provides feedback to the user, letting them know that the app is working on something in the background.

Using Suspense with a Custom Loading Indicator:

tsxCopyEdit// Custom Loading Spinner Component
function LoadingSpinner() {
  return <div className="spinner">Loading...</div>;
}

// Page Component using Suspense
export default function Page() {
  return (
    <Suspense fallback={<LoadingSpinner />}>
      <YourComponent />
    </Suspense>
  );
}

In this example, a custom loading spinner is displayed until YourComponent is ready.

6. Handling Async Data Fetching with Suspense

When it comes to data fetching, Suspense provides a more declarative and seamless way to manage async operations. Rather than manually managing loading states and error handling, Suspense allows you to focus on the actual rendering of your data.

You can use Suspense with React Query, GraphQL, or any async function to wrap your data fetching logic inside the Suspense boundary. The fallback UI is shown until the data is ready.

Example with React Query:

tsxCopyEditimport { useQuery } from 'react-query';
import { Suspense } from 'react';

function fetchUserData() {
  return fetch('https://api.example.com/user').then((res) => res.json());
}

function User() {
  const { data } = useQuery('user', fetchUserData);

  return <div>{data.name}</div>;
}

export default function Page() {
  return (
    <Suspense fallback={<div>Loading User...</div>}>
      <User />
    </Suspense>
  );
}

Here, we are fetching user data with react-query and displaying a loading state using Suspense.

7. Optimizing User Experience with Loading States

The purpose of Suspense is not just to show a loading state; it’s to enhance the user experience by showing informative, visually appealing, and non-blocking loading states. Here are some tips for optimizing the loading experience:

• Progressive Loading: For large data sets or components, show a loading progress bar or skeleton screens that mimic the content structure while it’s loading.
• Use Placeholders: Instead of showing a blank screen, use skeleton loaders or placeholders to simulate content until it loads.
• Conditional Fallbacks: Display different fallbacks based on what data or component is being loaded.

8. Best Practices for Loading UIs and Suspense Boundaries

• Modularize Suspense Boundaries: Split large Suspense boundaries into smaller ones to avoid blocking the entire app when a part of it is still loading.
• Provide Meaningful Feedback: The loading state should provide context to users — tell them what’s loading instead of a generic loading spinner.
• Error Boundaries: Use error boundaries to handle cases where the component fails to load or the async task encounters an error.

9. Conclusion

Integrating Suspense with App Router in Next.js is an excellent way to manage asynchronous operations and improve the user experience by handling loading states gracefully. By using Suspense boundaries, you can manage dynamic content, data fetching, and lazy loading with minimal code while ensuring your application remains performant and responsive.

To get the best results, combine Suspense with client-side rendering and server-side rendering for optimal user experience. Always remember to provide clear, informative loading states to your users to create a seamless and engaging app experience.