React 19: New Features and Examples

React 19 is the latest version of the popular JavaScript library for building user interfaces. It introduces a number of new features that are designed to make it easier and more efficient to build React applications. In this article, we will discuss some of the most important new features in React 19, providing examples of their use.

1. Concurrent Rendering

One of the biggest new features in React 19 is concurrent rendering. This feature allows parts of a component to be rendered without blocking the rendering of the rest of the component. This means that React applications can be more responsive and fluid, even when they are performing complex operations.

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

  return (
    <div>
      <p>Count: {count}</p>
      <button onClick={() => setCount(count + 1)}>Increment</button>
      {/* This part of the component will be rendered concurrently */}
      {count % 2 === 0 && <p>The number is even</p>}
    </div>
  );
}

In this example, when the user clicks the button, the App component will be re-rendered. However, the rendering of the part of the component that contains the text "The number is even" will be done concurrently, which means that the counter will be updated immediately, and the text "The number is even" will appear slightly later.

2. State Improvements

React 19 also introduces several improvements to how state is managed in React applications. The new features include:

• useState improvements: The useState hook is now more efficient and easier to use.
• New useLayoutEffect and useCallback hooks: These new hooks provide more control over when and how components are updated.
• Context improvements: React context has been improved to make it easier to share data across an application.

3. Lazy Components

React 19 also introduces lazy components. This feature allows components to be loaded dynamically, which can improve the performance of applications, especially for large applications.

const MyComponent = () => import('./MyComponent');

function App() {
  const [showComponent, setShowComponent] = useState(false);

  return (
    <div>
      <button onClick={() => setShowComponent(true)}>Show Component</button>
      {showComponent && <MyComponent />}
    </div>
  );
}

In this example, the MyComponent component will only be loaded when the user clicks the button. This can help improve the performance of the application if the MyComponent component is used infrequently.

4. Portals

React 19 also introduces a new feature called portals. Portals allow React components to be rendered outside of the DOM tree. This can be useful for components that need to be displayed in non-standard locations, such as modal dialogs or dropdowns.

import { createPortal } from 'react-dom';

function Modal() {
  return (
    <div className="modal">
      <h2>Modal Dialog</h2>
      <p>Modal dialog content</p>
    </div>
  );
}

function App() {
  return (
    <div>
      <button onClick={() => ReactDOM.createPortal(<Modal />, document.getElementById('modal-root'))}>
        Open Modal
      </button>
      <div id="modal-root"></div>
    </div>
  );
}

In this example, the Modal component will be rendered outside of the DOM tree into the div element with the ID modal-root.

Summary

React 19 is a significant update to the popular JavaScript library for building user interfaces. The new features, such as concurrent rendering, state improvements, lazy components, and portals, are designed to make it easier and more efficient to build React applications.