The Future of React with Suspense and Concurrent Features

Anton Ioffe - November 21st 2023 - 10 minutes read

Dive into the world of React as we explore the untapped potential of Suspense and concurrent features, poised to redefine how we craft high-performance user interfaces. This article takes you beyond the basics into the future of React development, where seamless user experiences are a reality, and the dreaded jank is a remnant of the past. From gracefully migrating to cutting-edge concurrent rendering techniques to mastering the art of performance tuning through Transitions and batching, we'll guide you through a landscape brimming with possibilities. Prepare to discover the practical harmonization of client and server-side patterns, and navigate the intricate balance between optimal performance and over-engineering. This journey is not just about adopting new paradigms—it's about avoiding the pitfalls that ensnare even the most seasoned developers, and emerging with a profound understanding of React's evolving ecosystem. Join us to unlock the full potential of your React applications, in an era where fluid interfaces are not just desired, they're expected.

Embracing Concurrency: Unlocking Performant UIs with React Suspense and Concurrent Features

In the realm of React development, concurrency is a paradigm shift that equips developers with the tools to craft user interfaces that can carry out multiple tasks simultaneously, without locking up the main thread. This advancement is crucial in an era where user experience defines the success of an application. By leveraging concurrent features, React developers can now intertwine user interactions and state updates, ensuring a seamless experience even when complex computations are underway. React's concurrent mode is not merely an add-on; it's a reimagined engine under the hood, designed to keep the UI responsive and fluid.

React Suspense is a hallmark feature that epitomizes the ethos of concurrency within React's ecosystem. Through Suspense, managing asynchronous operations becomes a declarative and streamlined process, replacing the convoluted logic that once plagued the management of loading states. By design, Suspense allows developers to specify what the UI should present during data fetching or other delay-prone operations. This minimizes unwieldy code and helps maintain a clean component tree, providing developers with a powerful abstraction to create frictionless loading sequences that enhance the user's sense of immediacy and engagement.

Concurrent rendering forms the backbone of these performance gains, managing UI work with finesse and precision. It achieves this through techniques like priority queuing and multi-versioning of the UI state. These strategies nurture a non-blocking UI that enacts changes with minimal disruption, queuing up updates and rendering them based on the priority of user actions. For example, typing in a search input should feel instantaneous, while loading secondary data in the background remains unobtrusive to the user's primary task. Here, concurrency excels by ensuring the interface remains nimble and quick to react.

Adopting these concurrent features can introduce a layer of complexity, especially for library authors, since components might behave differently when wrapped within the context of Concurrent Mode. This transition ushers in a new set of considerations around consistency across concurrent and non-concurrent portions of an application, urging developers to think holistically about state management and side effects. However, the advantage lies squarely with the end-user experience, as concurrent capabilities promise a smoother, more intuitive interaction model.

Looking forward, the React team continues to invest in concurrency as it wields the potential to reshape the landscape of UI development. The evolution of tools, like automatic batching and streaming server rendering, promises even more sophisticated enhancements in user interfaces. As developers embrace these concurrent features, they'll uncover fresh opportunities to innovate, pushing the boundaries of what’s expected from modern web applications. React Suspense and concurrent rendering are more than features; they represent a progressive blueprint for the future of interactive UIs, paving the way for experiences that feel as responsive as applications native to our devices.

When migrating to React 18, teams should first focus on ensuring their application runs on the new version without introducing any breaking changes. This involves a careful upgrade of the React and ReactDOM packages, followed by thorough testing to catch any potential discrepancies in behavior. Addressing this foundational step requires diligence but typically does not necessitate immediate refactoring to leverage concurrent features.

Adopting the new StrictMode is the second phase of migration. This development-phase feature helps in surfacing unwanted side-effects that could cause issues with concurrent rendering. It doubles down on lifecycle methods and render phases for components, making it easier to spot non-idempotent operations. By taking advantage of this mode, developers gain visibility into parts of their application that may not conform to the best practices required for a smooth transition to concurrent features.

As developers adapt to StrictMode, they can begin to refactor their code with an eye towards concurrency. Hooks such as [useTransition]( and useDeferredValue become instrumental at this stage. For example, implementing useTransition allows non-urgent updates, such as user-triggered navigations, to proceed without interrupting urgent UI tasks. This is a vital step in progressively introducing concurrent patterns into an application.

However, integrating hooks like useTransition requires judicious use within the application. A misstep often encountered is the indiscriminate application of useTransition across state updates. Best practices dictate using this hook selectively, where it adds real value to the user experience by preventing blocking UI updates. It's important to wrap only necessary actions, ensuring interactivity remains seamless without overcomplicating state updates.

In the last stage of migration, teams should rethink their approach to state management, side effects, and data-fetching in the context of React's concurrent capabilities. By way of example, consider the responsible integration of data-fetching within a Suspense component, ensuring that fetching only occurs when necessary and is not triggered on every render:

import React, { Suspense, useState, useEffect } from 'react';

function MyComponent() {
    const [dataResource, setDataResource] = useState(null);

    useEffect(() => {
        // fetchData should be a function that returns a resource
        // capable of integrating with React Suspense.
        const resource = fetchData('api/data');
    }, []); // Empty dependency array ensures fetch is only done on mount

    if (!dataResource) {
        return <div>Loading...</div>;

    return (
        <Suspense fallback={<div>Loading more...</div>}>
            <DataDisplay resource={dataResource} />

function DataDisplay({ resource }) {
    const data =; // Assume read() is a Suspense compatible call
    return <div>{data}</div>;

Adopting this kind of pattern shifts your codebase towards the asynchronous model of concurrent React. This mindset leads to not only immediate improvements in user experience but also a foundation that is well-suited for the evolving future of React's concurrent features.

React Suspense in Action: Client and Server Patterns

React Suspense streamlines client-side data fetching, orchestrating asynchronous requests to allow for a non-blocking UI. When integrating Suspense with data fetching libraries such as Relay or SWR, we observe distinct patterns. Relay leverages its container patterns with Suspense, offering a declarative approach to signal loading states. Conversely, SWR complements Suspense through its hooks by providing the needed data, error handling, and revalidation statuses to implement fallbacks during data fetching effectively. Consider the usage of Suspense around a data-driven component like so:

const UserProfileContainer = () => {
  const data = useUserData();
  // Suspense integrates with SWR or Relay internally in useUserData
  return data ? <UserProfile data={data} /> : null;

const ProfilePage = () => {
  return (
    <Suspense fallback={<div>Loading profile...</div>}>
      <UserProfileContainer />

On the server side, Suspense enables advanced loading strategies, such as partial hydration. It selectively defers heavy client-side rendering, maintaining performance and user interaction readiness. Server-rendered sections deliver the app's structural layout, with dynamic components staged for later, client-side rendering. Below is an example showcasing Suspense in use within a server-side rendering context:

// On the server
const AppSkeleton = () => (
    <Header />
    <Footer />

// On the client, after the app skeleton has been served
const DynamicContent = () => (
  <Suspense fallback={<ContentPlaceholder />}>
    <MainContent />

const App = () => {
  return (
      <AppSkeleton />
      <DynamicContent />

Error boundaries play a pivotal role when working with Suspense, as they provide a safety net for asynchronous operations. These constructs wrap around Suspense blocks, catching any thrown errors and preserving the application's stability. Here is a code snippet demonstrating the pairing of an error boundary with Suspense:

const ComponentWithErrorBoundary = () => (
  <ErrorBoundary fallback={<ErrorFallback />}>
    <Suspense fallback={<LoadingSpinner />}>
      <AsyncComponent />

const Application = () => (
  <ComponentWithErrorBoundary />

Suspending execution isn't always the optimal choice, notably in scenarios involving progressive loading of ancillary data or when handling intricate component interdependencies. Such use cases can require alternatives that avoid the potential complexities associated with Suspense.

Implementing Suspense in both client and server contexts demands meticulous integration, especially concerning error handling, to deliver a consistent, robust user experience while balancing the architectural intricacies and complexity.

Performance-Tuning with Transitions and Batching: The Nuances of User Perceived Performance

React 18's innovative approach to performance-tuning is anchored in two pivotal features: transitions and automatic batching. Transitions in React allow developers to mark certain state updates as non-urgent, thereby informally categorizing updates into those that require immediate feedback and those that can be deferred. This nuanced understanding of update urgency helps deliver a smooth user experience, as it closely aligns with how users perceive performance. Immediate feedback is critical for actions such as keypresses, clicks, and form submissions, where users expect a rapid response. Conversely, transitions can be used to manage less critical updates that do not require instant visual confirmation, like updating suggestions in a typeahead search.

import { [startTransition]( } from 'react';

function SearchComponent({ inputValue, onChange }) {
    // Urgent: Update the input value in real-time
    const handleChange = (event) => {

    // Non-urgent: Fetch suggestions based on the input value
    const fetchSuggestions = (input) => {
        startTransition(() => {
            // Imagine fetchSuggestionsApi is a method that fetches search suggestions

    return (
            onKeyUp={() => fetchSuggestions(inputValue)}

Automatic batching further complements the tuning process by aggregating multiple state updates into a single re-render cycle. This innate feature of React 18 consolidates updates in various asynchronous contexts—such as promises, timeouts, and native event handlers—into one paint cycle, which can vastly diminish the number of renders and consequently, the perceptible jank in interactive elements.

import { useState } from 'react';

function Counter() {
    const [count, setCount] = useState(0);

    const increment = () => {
        setCount((c) => c + 1);
        setCount((c) => c + 1);

    // In older React versions, increment() would have caused two re-renders.
    // With React 18, these are batched into a single re-render for better performance.
    return (
            <p>Count: {count}</p>
            <button onClick={increment}>Increment count</button>

However, these enhancements come with a novel complexity. Developers must make informed decisions about what qualifies as urgent or non-urgent. Misuse of transitions can lead to sluggish interfaces if too many updates are marked as non-urgent, or it may not show a noticeable improvement if used sparingly. Similarly, while batching reduces re-renders, it also aggregates state changes which might introduce subtle bugs if the individual states are interdependent and expected to be resolved sequentially.

In navigating these trade-offs, it's essential to profile your application's performance and understand how these features impact your specific use case. Consider experimenting with transitions for various interactions and monitoring how they influence the user's perception of your app's responsiveness. Similarly, assess the impact of batching on complex component trees to optimize render cycles without compromising the application's logical flow or introducing unintended side-effects.

The ideal balance lies in the ability to predict and shape the user experience according to the user's expectations of urgency and immediacy. By effectively leveraging React 18's capabilities, developers can fine-tune applications, ensuring they remain rapid and robust, while simultaneously delivering a user experience that feels instantly responsive and seamlessly interactive.

The Pitfalls of Premature Optimization: Common Mistakes and Corrective Measures

Overzealous optimization can be the bane of adopting new technologies, and React's Suspense and concurrent features are no exception. A common mistake is to wrap too many components with Suspense, believing it to be a silver bullet for any performance issue. This can lead to a fragmented user experience, with many loading states that confuse rather than help. The corrective measure here is to use Suspense judiciously. Only large, data-heavy components where the user would expect a loading sequence should employ Suspense, ensuring a cohesive and intuitive user experience.

Another pitfall is misunderstanding the use of concurrent features like startTransition for state updates that aren't urgent. By marking every state update with startTransition, developers may inadvertently prioritize less important updates and degrade the UX. The best practice is to save startTransition for updates that do not require an immediate response, such as input from a typeahead search. Have you evaluated the urgency of the updates in your application and utilized startTransition accordingly?

Incorrect use of hooks is also a lurking danger when tapping into the power of React's concurrent world. For example, excessive reliance on useDeferredValue can make the UI feel sluggish, as updates to deferred values may lag behind user actions. Counter this by employing useDeferredValue when the deferred data isn't critical to immediate UI updates. This preserves the perception of speed while still postponing the less essential updates.

Developers new to Suspense may also fall into the trap of duplicating state logic. They might hold data fetching states within the component state, despite Suspense implicitly managing it. Eliminate this redundancy by fully embracing Suspense's capabilities, allowing it to handle the loading, error, and success states internally. Are you occasionally managing states that Suspense is designed to handle automatically?

Lastly, the temptation to use Suspense for every new feature can lead to overlooking more suitable existing solutions. Not every loading scenario requires Suspense. Some may benefit more from simple conditional rendering or using already matured patterns until Suspense is fully adapted for that use-case. It's essential to analyze the specific use cases and determine whether Suspense provides a tangible benefit over traditional methods. Are your current loading strategies truly optimized by incorporating Suspense, or would they function just as effectively with established techniques?


This article explores the future of React development with the introduction of Suspense and concurrent features. It discusses how these features enhance the performance of user interfaces by allowing multiple tasks to be carried out simultaneously without locking up the main thread. The article provides insights into the benefits of adopting these features, along with strategies for smooth migration and best practices for performance tuning. A challenging technical task for the reader is to implement the useTransition hook selectively in an application to improve user experience without overcomplicating state updates. This task encourages the reader to think critically and apply their understanding of concurrent React principles to optimize their own code.

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