Introducing React 19: What's New?

# React # Javascript

10 Mins

Jayram Prajapati · 07 May 2024

The most recent version of React was 18.2.0, which was released on June 14, 2022. React is a popular framework for creating apps and web pages. However, it has been some time since they released anything new, which has irritated some React users. React has now announced a new version in response to negative feedback from users.

April 2024 ended with a new raise in frontend development on the 25th. React announced the release of the beta version in npm to test new features and upgrades. You should upgrade to 18.3.0 and watch for React 19's stability, as the libraries are still in development based on customer input. As they explain, remember that React 19 is still in development. To keep up with the latest developments, follow the official guide on GitHub and the official team on social media.

Let’s clear every point covered in the React beta release documentation without wasting time.

App developers should wait for a stable release, but libraries can prepare for React 19.

What is new in React 19?

React 19 brings exciting changes! Actions have been introduced to make managing data updates easier. State management is streamlined via new hooks such as useActionState and useOptimistic. Error reporting, reference handling, and async script support have all improved.

Let's dive in and explore the one-by-one new features of React 19.

No 1. Actions: Handling Async Operations Simplified

Data mutations and updating the UI are common tasks in React apps. Previously, this process required manual management of various states, such as pending states (when waiting for a response from an API), error handling, optimistic updates (updating the UI optimistically before receiving the response), and sequential requests.

Here's an overview of how Actions make it easier to handle data changes:

Pending State Management: Actions automatically manage a pending state that indicates when a request is in progress. They set the pending state to true at the start of a request and reset it to false after the final state update is committed.
Optimistic Updates: With Actions, you can use the useOptimistic hook to provide users with instant feedback by updating the UI optimistically while the requests are still being submitted.
Error Handling: Actions also handle error scenarios. They provide built-in error-handling mechanisms, allowing you to display error boundaries when a request fails. Actions automatically revert optimistic updates to their original values if an error occurs.
Form Management: React 19 extends Actions to manage forms automatically. You can pass functions to the action and formAction props of the <form> element, which uses Actions by default. This simplifies form handling, and the form is reset automatically after submission.

No 2. New Hooks: useActionState and useOptimistic

React 19 adds new features to supplement Actions:

useOptimistic => One of the common pain points in web app development is the feeling of slowness for the user as they wait for requests to finish and things to load. useOptimistic is intended to help fight that by allowing us to easily add “optimistic” content while we wait for an async request to complete. Once we have the data, we can update any overly optimistic content that is no longer accurate.

useActionState => useActionState will accept a function and return a wrapped Action to call. When that wrapped Action gets called, useActionState will set the pending state of the Action as pending and return the last result of the Action as data. Those already experimenting with the Canary release might already be familiar with useActionState—although then it was going by the name useFormState. useFormState is now officially deprecated.

useFormStatus => UseFormStatus is a new hook introduced in React 19 that details the most recent form submission's status. This hook is especially helpful when used with Actions and <form> elements because it gives developers access to the submission's pending status, the data being submitted, and the HTTP method used.

UseFormStatus improves form submission visibility and control, allowing developers to respond dynamically to submission statuses and provide appropriate user feedback.

Explanation of how <form> Actions simplify form handling:

Automated State Management: <form> Actions automate the management of form submission states, including pending states and error handling. This simplifies the codebase and reduces the likelihood of errors related to manual state management.
Optimistic Updates: Actions support optimistic updates, allowing developers to update the UI optimistically while waiting for form submissions to complete. This provides a smoother user experience by providing immediate feedback to users.
Error Handling: Actions handle error scenarios automatically, allowing developers to focus on handling errors gracefully rather than managing error states manually.

Overall, integrating Actions with <form> elements and introducing useFormStatus streamline form handling in React 19, offering developers a more efficient and robust solution for managing form submissions and providing a better user experience.

React 19's new features and hooks make handling data mutations and updating the UI easier and less error-prone, as much of the manual state management is abstracted.

No 3. New API: use

The new use API, introduced in React 19, transforms how resources are accessed during rendering. Rich asynchronous data handling and context-based rendering are made easier by its ability to allow components to read resources like promises and context easily, all within the render function.

Example: Using use with Promises and Context

import React, { use } from 'react';

// Promise for fetching comments
const commentsPromise = fetchComments();

function Comments() {
  // Suspends until the promise resolves
  const comments = use(commentsPromise);

  return (
    <div>
      {comments.map(comment => (
        <p key={comment.id}>{comment}</p>
      ))}
    </div>
  );
}

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

In this case, the use API allows the Comments component to suspend until the commentsPromise is resolved. This improves perceived performance by guaranteeing the component renders only after the available data. The Heading component from previous examples serves as an example of how the use API can also be used to read context conditionally within the component hierarchy. API use increases React components' overall efficiency and flexibility, allowing you to incorporate resource reading into the render phase smoothly.

No 4. React Server Components

Web development has advanced significantly with React 19's introduction of server components. Here's an overview of server components and how they function:

Server Components in React 19: Server components (RSCs) are a new concept introduced in React 19. They allow developers to create components that run on the server rather than the browser. This change in execution allows for improved performance and scalability because server-side rendering can offload processing tasks from clients.

When a component is first rendered, it is executed on the server instead of traditional components that operate in the browser. This means that the server creates the HTML markup for these components, which is then delivered to the client for display. Server components offer the basis for server-side rendering and data processing, but client-side components can still manage updates and subsequent interactions.

Server Actions for Running Async Functions: Server Actions enhance Server Component functionality by allowing asynchronous functions to be executed on the server. This feature is especially useful for data retrieval, processing, and integration with external APIs or databases.

During the rendering stage, servers run the asynchronous functions defined by developers in Server Actions within Server Components. This allows Server Components to retrieve data or perform other asynchronous tasks before sending the rendered content to the user.

Server Actions improve performance and responsiveness by running async functions on the server and offloading data processing tasks from the client. Server Actions also make it easier to integrate server-side logic into components, increasing the flexibility and capabilities of Server Components.

Overall, Server Components and Server Actions represent a paradigm shift in React development, opening up new possibilities for server-side rendering, data processing, and web application performance optimization.

No. 5 Improvements in React 19

Ref as a Prop for Function Components: In React 19, function components can access refs directly as props, eliminating the need for forwardRef. This streamlines component development and enhances code readability.
Improved Error Reporting for Hydration Errors: React 19 improves hydration error reporting by offering comprehensive details and remediation recommendations. This improves debugging and ensures smoother application performance.
Support for Rendering <Context> as a Provider: React 19 supports rendering <Context> as a provider, resulting in a more concise syntax. This simplifies the implementation of context providers, enhancing code maintainability.
Cleanup Functions for Refs: React 19 supports returning cleanup functions from ref callbacks, allowing for more efficient resource management. This improves code robustness by ensuring that components are cleaned up when unmounted.
UseDeferredValue Initial Value: React 19 includes an initialValue option for useDeferredValue, which allows components to specify initial values for deferred state updates. This improves user experience by giving them more control over rendering behavior.

No 6. Support for Document Metadata and Stylesheets

React 19 now supports rendering document metadata tags such as <title>, <link>, and <meta> directly within components. React 19 also includes built-in support for managing external and inline stylesheets within the component hierarchy.

Rendering Document Metadata Tags Natively: React 19 allows components to use document metadata tags like <title>, <link>, and <meta> directly in their JSX structure. When these components are rendered, React moves the metadata tags to the <head> section of the document, ensuring proper handling across various rendering scenarios.

Built-in Support for Stylesheets: With built-in support for both inline (<style>...</style>) and external (<link rel="stylesheet" href="...">) styles, React 19 makes managing stylesheets easier. This feature lets you include stylesheets directly in component definitions, ensuring proper style ordering and handling during rendering.

import React from 'react';

function MyComponent() {
  return (
    <div>
      {/* Document Metadata */}
      <title>My Page Title</title>
      <meta name="description" content="This is my page description" />

      {/* Stylesheets */}
      <link rel="stylesheet" href="styles.css" />
      <style>
        {`
          .container {
            background-color: #f0f0f0;
            padding: 20px;
          }
        `}
      </style>

      {/* Content */}
      <div className="container">
        <h1>Welcome to My Website</h1>
        <p>This is the content of my website...</p>
      </div>
    </div>
  );
}

MyComponent renders document metadata tags (<title> and <meta>) with external and inline stylesheets. React ensures that these components are rendered and managed correctly, improving the component's flexibility and maintainability.

No 7. Support for Async Scripts and Resource Preloading

React 19 makes handling scripts in your components easier, particularly async scripts that load in random order. It was previously difficult to position them deep within your component tree. React allows you to place async scripts anywhere without worrying about duplication or relocation.

function MyComponent() {
  return (
    <div>
      <script async={true} src="..." />
      Hello World
    </div>
  )
}

function App() {
  return (
    <html>
      <body>
        <MyComponent />
        {/* won't lead to duplicate script in the DOM */}
        <MyComponent />
      </body>
    </html>
  )
}

React makes sure that async scripts are loaded and run only once in every scenario, even when several components render them. Async scripts are inserted into the of a page during Server Side Rendering, and they are given a lower priority than essential resources to speed up pages.

Support for Preloading Resources: React 19 introduces new APIs for more efficient resource loading. These APIs, such as prefetchDNS, preconnect, preload, and preinit, aid in the early loading of fonts, stylesheets, and scripts, resulting in improved page performance.

import { prefetchDNS, preconnect, preload, preinit } from 'react-dom'

function MyComponent() {
  preinit('https://.../path/to/some/script.js', { as: 'script' }) // loads and executes this script eagerly
  preload('https://.../path/to/font.woff', { as: 'font' }) // preloads this font
  preload('https://.../path/to/stylesheet.css', { as: 'style' }) // preloads this stylesheet
  prefetchDNS('https://...') // for hosts not requested immediately
  preconnect('https://...') // for anticipated requests
}

These APIs improve initial page loads by moving resource discovery out of stylesheet loading and client updates by prefetching resources for anticipated navigation, resulting in a smoother user experience.

No 8. Compatibility with Third-party Scripts and Better Error Reporting

Hydration is the process of adding client-side functionality, such as event listeners, to markup that is rendered by a server. Maintaining functionality and consistency between server-rendered and client-rendered content is critical when integrating third-party scripts with React applications. Proper hydration is essential for this.

The hydration process has been improved, focusing on increasing compatibility with third-party scripts. The enhancements guarantee the smooth integration of external scripts with React components, facilitating dependable hydration and uniform performance in server and client-rendered elements.

React 19 improves third-party script hydration, allowing developers to use various tools and functionalities while maintaining performance and stability.

Better Error Handling and Reporting:

React 19 improves error reporting and handling, giving developers more useful and actionable error messages when problems arise in their apps. These upgrades also improve debugging and enable developers to find and fix errors more efficiently.

Developers can expect better error handling and reporting in React 19.

More descriptive error messages: React 19 provides clearer and more detailed error messages, helping developers pinpoint the root cause of issues more quickly.
Improved stack traces: Error stack traces are enhanced to provide better context and traceability, making it easier to trace the execution flow and identify problematic areas within the codebase.
Enhanced error boundary support: React 19 strengthens support for error boundaries, allowing developers to encapsulate error-prone components and gracefully handle errors without compromising the stability of the entire application.
Integration with developer tools: Error reporting in React 19 is designed to seamlessly integrate with developer tools, providing a cohesive debugging experience across different environments and workflows.

No 9. Support for Custom Elements

Custom elements are now fully supported in React 19, addressing previous issues with their use in React applications. This is how React 19 handles custom elements and enhances their integration:

Server-Side Rendering: During server-side rendering (SSR), React 19 differentiates props passed to a custom element based on their type:

Props with primitive values like strings, numbers, or the value true will render as attributes.
Props with non-primitive types, such as objects, symbols, functions, or the value false, will be omitted.

This strategy ensures that only props suitable for attributes are rendered as such during SSR, maintaining compatibility with custom element specifications while optimizing performance.

Client-Side Rendering:

When rendering custom elements on the client side, React 19 assigns props to properties that match existing properties on the custom element instance. A prop is assigned as an attribute if it does not match a property.

Props are correctly mapped to properties and attributes based on their compatibility with the custom element's API, allowing React to integrate custom elements into client-side rendering seamlessly.

This improved compatibility increases React components' versatility and extensibility, allowing seamless integration with custom elements and creating more dynamic and feature-rich user interfaces.

Essence

These are the words from the React development team experts to the developers. The development team members work collaboratively to create and maintain high-quality code for the React project.

We'll see many new features in React 19, but we'll have to wait longer for the compiler. This means the team is also working on the React compiler. React 19 will include improvements to performance, developer experience, and overall usability. The React team is always looking for ways to improve the library and give developers access to state-of-the-art resources for creating dynamic user interfaces.

However, as the reports and excitement of the React team show, they will introduce us to the React compiler by the end of this year. Elightwalk team gives you a clear report on the latest updates and developments in React, including the progress on the React compiler. Keep checking back for more details on how this new feature will improve your experience with React development.

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Jayram Prajapati

Full Stack Developer

Jayram Prajapati brings expertise and innovation to every project he takes on. His collaborative communication style, coupled with a receptiveness to new ideas, consistently leads to successful project outcomes.

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