React has consistently advanced to satisfy the increasing expectations of modern web applications while offering potent tools that aid developers in using fast, responsive and user-friendly experiences. In this context, the most significant impact of new React features has been made by Suspense and Concurrent Features. These two features indicate a transition towards smarter rendering strategies that allow the developer to avoid managing asynchronous behaviors in a more efficient and seamless manner.
In this article we will explore what React Suspense and Concurrent Features are, what they are doing, and how to use them in a realistic application.
What is React Suspense?
React Suspense is a mechanism designed to handle asynchronous workflows in a manner that feels natural within the React rendering workflow. Released docketed with React.lazy (for lazy loaded components), Suspense has quickly evolved to accommodate additional use cases, particularly with data fetching and asynchronous rendering.
Suspense leverages the ability for components to “suspend” rendering a component when an operation is pending. For instance The react app could indicate it is still loading when it is waiting for a code chunk to load, or waiting to fetch data from API (this is pending state). During this load time, the application can show a “fallback” UI (like a spinner or placeholder). Then when the pending state is done and has loaded the code chunk or data, React will render the full content.
Suspense Note: Common Use Cases
- Lazy Evaluating Components: By dynamically importing components, the benefit will be a decrease in the initial JS bundle and reduced Time to First Paint (TTFP).
- Data Fetching: Next.js with React Suspense support libraries (Relay or React Query) enables you to declaratively specify loading and data fetching states.
- Streaming Server-Side Rendering (SSR): Suspending provides another level of server rendering by giving React access to streaming pieces of your UI based on data availability.
With Suspense, as you are determining the boundary at which loading might occur, you have a mandate to structure how you manage asynchronicity but also deliver a beautiful and predictable UI.
What are Concurrent Features?
Concurrent features, present in React v18 and released in stages, represent features that help React interrupt itself and thus prioritize rendering work. Traditionally, this model uses synchronous rendering, where the main thread blocks until it finishes rendering a component into the DOM. But with Concurrent features, rendering becomes interruptible and more responsive to your user’s interactions with your UI.
Instead of a separate “mode” like the experimental Concurrent Mode or earlier versions in React, the concurrent features now integrated into React are incremental and are available for usage without an entire commitment to concurrent mode.
Main Concepts and Tools in Concurrent Features
Automatic Batching: React can automatically group multiple state updates into a single render, so we won’t have to render the whole page unnecessarily.
startTransition: This function lets you mark some updates as non-urgent. For instance, when filtering a large list of items due to user input, we can defer the costly filtering process so we don’t lock the input field.
useDeferredValue: This hook lets you defer updating a piece of state until the browser has some extra time, which is great for avoiding jank while you handle interactions.
Streaming SSR: This allows the application to render part of the page and send to the browser, while the rest continues to be lazily loaded. This helps the perceived performance of large applications.
These features enable developers to build applications that remain responsive during complex rendering logic or when handling large data sets.
Benefits of Using Suspense and Concurrent Features
React Suspense and Concurrent Features have many advantages that align with today’s performance and user experience aspirations:
Faster Applications: Applications can operate much more quickly and responsively thanks to its ability to postpone non-essential tasks and render more effectively.
Better User Experience: Nothing is blocking critical interactions, even while other parts of the application are still loading or updating.
Easier Asynchronous Logic: These features allow more declarative answers to asynchronous behavior, like data fetching or code splitting.
Fine-Grained Control Over UI Rendering: Being able to dictate which parts of the UI are critical, and which ones can wait, provides developers with even deeper control of rendering.
Best Practices to Keep in Mind when Using Suspense and Concurrent Features
To maximize the benefits of these features, consider introducing these best practices into your development workflow:
Use Suspense as a way to define clear Async Boundaries: Whether lazy-loading components or fetching data, Suspense allows you to define the loading states and when they show up in your UI.
startTransition to wrap non-critical updates: To improve responsiveness when filtering, sorting, or updating complex views that aren’t immediately needed, use startTransition so the user can keep interacting with your app.
Use data-fetching libraries that support Suspense declaratively: Libraries like React Query, and Relay, can utilize Suspense’s declarative APIs right out of the box, and take care of managing load and error states.
Monitor performance to optimize: Use tools such as the React DevTools Profiler to see how your app renders and if/where you may have bottlenecks. This information will help you determine where you can leverage Suspense and concurrent updates in your apps.
Use Suspense sparingly in a deeply nested tree of components: Although suspense has a lot of potential, it can occasionally result in fragmented loading behavior when applied to deeply nested components. When you can, keep fallback UI centralized.
Conclusion
React Suspense and Concurrent Features present a genuine step change in frontend architecture. By taking advantage of these features, engineers can build applications that are both fast and performant, while matching the needs of users during an experience. Heavily reliant on the developer, Suspend and concurrent features dissuade imperatively building loading logic for components. Instead, one can declaratively design, and provide an intuitive UI where things work seamlessly on both user/application state appearance be it data or visual.
As the React ecosystem continues to evolve, React developers will certainly need to understand these tools to build scalable, performant, modern web applications. If you are optimizing an old app or building a new app considering Suspense and Concurrent Features may save you time and provide a better end user experience as well.
Contact Us Today
