A deep dive into React's experimental_SuspenseList and its manager, exploring its role in coordinating loading states and improving perceived performance for modern applications.
React's Suspense component has revolutionized how we handle asynchronous operations and loading states in our applications. The experimental_SuspenseList takes this a step further by providing a mechanism for orchestrating the display of multiple Suspense boundaries. This blog post will explore experimental_SuspenseList, its manager, and how to effectively use them to create a smoother, more predictable user experience, particularly when dealing with data fetching and resource loading. This is still an experimental API, so exercise caution when using in production, as the API may change.
Understanding React Suspense
Before diving into experimental_SuspenseList, it's crucial to understand the fundamentals of React Suspense. Suspense is a component that allows you to "suspend" rendering until a promise resolves. This is particularly useful for data fetching. Instead of displaying a blank screen or a loading spinner while data is being fetched, you can wrap the component that depends on the data within a Suspense boundary and provide a fallback component to display while the data is loading.
Here's a basic example:
import React, { Suspense } from 'react';
// A component that suspends until data is fetched
function MyComponent() {
const data = useResource(fetchData()); // Hypothetical useResource hook
return
Data: {data}
;
}
function App() {
return (
Loading...
}>
);
}
In this example, MyComponent uses a hypothetical useResource hook to fetch data. If the data is not yet available, the component suspends, and React displays the fallback (
Loading...
) until the data is resolved.
Introducing experimental_SuspenseList
experimental_SuspenseList is a component that allows you to coordinate the display of multiple Suspense boundaries. This is particularly useful when you have a list of items that each depend on asynchronous data. Without SuspenseList, the items might appear in a jumbled order as their data becomes available. SuspenseList allows you to control the order in which the items are revealed, improving the perceived performance and user experience.
experimental_SuspenseList is considered experimental, so you must import it from the experimental channel:
import { unstable_SuspenseList as SuspenseList } from 'react';
revealOrder Prop
The most important prop for SuspenseList is revealOrder. This prop determines the order in which the Suspense boundaries within the SuspenseList are revealed. It accepts one of the following values:
forwards: Reveals the Suspense boundaries in the order they appear in the component tree.
backwards: Reveals the Suspense boundaries in the reverse order they appear in the component tree.
together: Reveals all Suspense boundaries simultaneously once all the data is available.
Example with revealOrder="forwards"
Let's say you have a list of product cards, and each card needs to fetch product details. Using revealOrder="forwards" ensures that the cards appear from top to bottom as their data loads.
import React, { Suspense, unstable_SuspenseList as SuspenseList } from 'react';
function ProductCard({ productId }) {
const product = useResource(fetchProduct(productId)); // Hypothetical fetchProduct function
return (
In this example, the product cards will load one after the other from top to bottom, creating a more visually pleasing and predictable experience.
Example with revealOrder="backwards"
Using revealOrder="backwards" would reveal the product cards from bottom to top. This might be useful in scenarios where the most important information is at the bottom of the list.
Example with revealOrder="together"
Using revealOrder="together" would wait until all product data is loaded before displaying any of the cards. This can be useful if you want to avoid layout shifts or if you need all the data to be available before the user can interact with the list.
Introducing the experimental_SuspenseList Manager
While experimental_SuspenseList provides a way to coordinate Suspense boundaries, managing more complex scenarios can become challenging. The experimental_SuspenseList Manager offers a more structured approach to managing these coordinated loading states.
Unfortunately, there isn't a built-in "experimental_SuspenseList Manager" component directly provided by React. Instead, the term usually refers to strategies and patterns for managing the coordination of multiple SuspenseLists, especially in complex scenarios, which can be considered as creating your own manager. Here's how you can approach creating a custom manager:
Conceptualizing a Custom Manager
The core idea is to create a component or a set of hooks that encapsulate the logic for controlling the reveal order, handling errors, and providing a consistent loading state to its children. This manager component acts as a central point for coordinating the SuspenseLists within your application.
Benefits of a Custom Manager
Centralized Logic: Consolidates the logic for managing SuspenseLists in one place, making your code more maintainable and easier to understand.
Customizable Behavior: Allows you to tailor the reveal order, error handling, and loading states to the specific needs of your application.
Improved Reusability: Enables you to reuse the manager component across multiple parts of your application, promoting consistency and reducing code duplication.
Building a Simplified Manager
Here's an example of a simplified custom manager component:
import React, { useState, createContext, useContext, unstable_SuspenseList as SuspenseList } from 'react';
// Create a context for managing the reveal order
const RevealOrderContext = createContext();
// Custom manager component
function SuspenseListManager({ children, defaultRevealOrder = "forwards" }) {
const [revealOrder, setRevealOrder] = useState(defaultRevealOrder);
const contextValue = {
revealOrder,
setRevealOrder,
};
return (
{children}
);
}
// Custom hook for accessing and updating the reveal order
function useRevealOrder() {
const context = useContext(RevealOrderContext);
if (!context) {
throw new Error("useRevealOrder must be used within a SuspenseListManager");
}
return context;
}
// Example usage
function App() {
const productIds = [1, 2, 3, 4, 5];
const { revealOrder } = useRevealOrder();
return (
{productIds.map((productId) => (
Loading product...
}>
))}
);
}
function ProductCard({ productId }) {
const product = useResource(fetchProduct(productId)); // Hypothetical fetchProduct function
return (
{product.name}
{product.description}
);
}
In this example:
A RevealOrderContext is created to manage the reveal order state.
The SuspenseListManager component provides the context value, including the current reveal order and a function to update it.
A useRevealOrder hook is created to consume the context value within the children components.
Expanding the Manager
This basic manager can be extended with additional features, such as:
Error handling: Manage errors within the SuspenseList and display error messages to the user.
Custom loading indicators: Provide more specific loading indicators for different parts of the application.
Performance optimizations: Implement techniques to improve the performance of the SuspenseList, such as memoization and lazy loading.
Advanced Use Cases and Considerations
Nested SuspenseLists
You can nest SuspenseList components to create more complex coordination scenarios. For example, you might have a SuspenseList for a section of the page and another SuspenseList for the individual items within that section. The outer SuspenseList can control the order in which the sections appear, while the inner SuspenseList can control the order in which the items within each section appear.
Transitions
When using SuspenseList, consider using React's useTransition hook to create smoother transitions between loading states. useTransition allows you to defer updates, which can prevent jarring layout shifts and improve the overall user experience.
Error Boundaries
It's important to wrap SuspenseList components within error boundaries to catch any errors that might occur during data fetching or rendering. Error boundaries prevent the entire application from crashing and allow you to display a graceful error message to the user.
Server-Side Rendering (SSR)
Suspense and SuspenseList can be used with server-side rendering, but it's important to be aware of the limitations. When rendering on the server, you need to ensure that all the necessary data is available before sending the HTML to the client. Otherwise, the client might need to re-render the component, leading to a poor user experience.
Best Practices
Use descriptive fallbacks: Provide informative fallbacks that tell the user what's happening while the data is loading.
Optimize data fetching: Ensure that your data fetching logic is efficient and avoids unnecessary requests.
Consider the user experience: Choose a revealOrder that makes sense for your application and provides a smooth, predictable user experience.
Test thoroughly: Test your SuspenseList components with different data loading scenarios to ensure that they behave as expected.
Monitor performance: Use React DevTools to monitor the performance of your SuspenseList components and identify any bottlenecks.
Conclusion
experimental_SuspenseList provides a powerful way to coordinate the display of multiple Suspense boundaries and improve the perceived performance of your React applications. By understanding the fundamentals of Suspense, the revealOrder prop, and building custom managers, you can create a smoother, more predictable user experience, especially when dealing with data fetching and resource loading. Remember that this is an experimental API, so be sure to stay updated with the latest React documentation and consider the potential for API changes. By carefully considering these factors, you can leverage experimental_SuspenseList to build more engaging and performant React applications. As React evolves, these patterns will likely solidify into more concrete APIs, but understanding the underlying principles is crucial for building robust and user-friendly applications.