How React 18 improves app performance.

React is one of the most popular JavaScript libraries for building user interfaces. It is constantly evolving and improving, and the new version, React 18, has introduced some significant changes. In this article, we will try to explore some of these changes.

Concurrent Mode.

Concurrent Mode is one of the most anticipated features introduced in React 18. It aims to improve the performance and responsiveness of applications, especially when rendering components takes a significant amount of time. We will explore what Concurrent Mode is, how it works, and how to use it in practice.

What is competitive mode?

Concurrent Mode is a new operational mode in React that allows more efficient utilization of CPU resources and accelerates the process of rendering components. It works by breaking down long operations into shorter ones and executing them in parts. This enables the browser to remain unblocked and continue displaying the user interface even during the execution of additional operations.

How does competitive mode work?

Concurrent Mode works by breaking down the rendering process into several stages that are executed in a non-blocking manner. This allows the browser to remain unblocked and continue displaying the user interface even during the execution of additional operations.

In React 18, a new feature called createRoot() has been introduced, which allows creating a root component in Concurrent Mode. To do this, you need to pass the concurrent: true flag `concurrent: true` as the second argument when creating the root component:

Now the program will work in Concurrent Mode.

Concurrent Mode can also be used for lazy loading of components.

To do this, you need to use the lazy() function:

The lazy() function takes a function that returns a promise with the component. When the component is ready, it will be displayed. Otherwise, a fallback component will be shown.

Concurrent Mode is a powerful tool to improve the performance and speed of React applications. It allows the browser not to block and continue displaying the user interface even during the execution of long operations. To use Concurrent Mode, you need to create a root component with the concurrent: true flag and use the useTransition() hook or the lazy() function.

In summary, Concurrent Mode and lazy loading are important features introduced in React 18 to optimize the rendering process and enhance user experience, making React applications faster and more efficient. By leveraging these new capabilities, developers can create smoother, more responsive web applications.

Automatic batch updates for asynchronous operations.

React 18 introduces a new feature that allows you to automatically group component state updates for asynchronous operations. This means that React will collect all the state updates that occurred during the execution of the asynchronous operation and apply them in one shared update.

How does automatic batching work?

Automatic batching works by collecting all state updates that occurred during the execution of an asynchronous operation and applying them as a single batched update after the operation is complete. This helps avoid multiple re-renders of components and improves application performance.

Let's take a look at a few code examples to understand how to use automatic batching in practice.

Using setState() inside setTimeout().

Let's consider an example where we use setState() inside setTimeout(). In this case, React automatically batches the state updates that occurred during the execution of setTimeout().

In this example, we use setTimeout() to set two state updates. However, thanks to automatic batching, React will apply them as a single combined update after the setTimeout() is completed.

Using fetch().

Let's consider an example where we use fetch() to fetch data and set a state update after receiving the data. In this case, React also automatically batches the state updates.

In this example, we use fetch() to fetch data and set a state update after receiving the data. However, thanks to automatic batching, React will apply this state update as a single batch after the fetch() is completed.

Automatic batching is a new feature in React 18 that allows automatic grouping of state updates for asynchronous operations. It helps improve performance and prevents unnecessary component re-renders. To use automatic batching, you need to use setState() or useReducer() functions inside asynchronous operations, such as setTimeout() or fetch().

The useDeferredValue hook.

React 18 introduced a new hook called useDeferredValue, which allows deferring state updates of a component until they are needed. This can be useful for improving performance and preventing unnecessary component re-renders.

How does useDeferredValue work?

The useDeferredValue function works by creating a deferred version of the component's state value. This deferred version is used during component rendering instead of the actual value until the moment when the value needs to be updated. When that happens, React compares the real value with the deferred version, and if they differ, the component gets updated.

Let's take a look at a few code examples to better understand how to use useDeferredValue in practice.

Using useDeferredValue with useState().

Let's take an example of using useDeferredValue with useState(). In this case, we defer the state update until the moment the user finishes entering text into the input field.

In this example, we use useDeferredValue with useState() to defer updates of the text state values. We also pass the option timeoutMs: 1000 to set the delay time in milliseconds before updating the values.

Using useDeferredValue with useReducer().

Let's consider an example where we use useDeferredValue with useReducer(). In this case, we defer the updates of the state until the moment the user finishes reloading the list of items.

In this example, we use useDeferredValue together with useReducer() to defer the updates of the state value. We also pass the option timeoutMs: 1000 to set the delay time in milliseconds before applying the updates.

useDeferredValue is a new hook in React 18 that allows deferring the updates of a component's state until it is necessary. This can be useful for improving performance and avoiding unnecessary component re-renders. To use useDeferredValue, you need to pass it the state value and the timeoutMs option to set the delay time before applying the update.

SSR improvements in React 18.

React 18 offers several enhancements for Server-Side Rendering (SSR) that can significantly improve performance and user experience. We will explore these enhancements and provide examples of code for their implementation.

Preliminary rendering.

React 18 introduces a new feature called "pre-rendering," which allows rendering components on the server before they are displayed on the client. This can significantly reduce page loading time and improve SEO.

To use pre-rendering in React 18, you can utilize the new method "renderToNodeStream()".

Here's an example code:

In this example, we use renderToNodeStream() to render the "App /" component on the server and send it as a streaming response. We also add basic HTML markup and close it after the streaming response is complete.

Using Suspense for SSR.

In React 18, there are also improvements for using Suspense in SSR. Now you can use Suspense to wait for data loading on the server and display a fallback (placeholder) until the data becomes available.

Here is an example code:

In this example, we use Suspense to wait for data loading on the server before rendering the "AsyncComponent /". We also add a fallback (placeholder) "div"Loading..."/div" that will be displayed until the data becomes available.

Using useOpaqueIdentifier for SSR.

In React 18, a new hook called useOpaqueIdentifier was added, which allows generating unique identifiers on both the server and the client. This can be useful for SSR when there is a need to create unique identifiers on the server for later use on the client.

Here's an example of the code:

In this example, we use useOpaqueIdentifier() to create a unique identifier on the server during the rendering of the "App /" component. We also pass the generated identifier in the HTML code, which will be used on the client.

React 18 introduces several improvements for server-side rendering (SSR) that can significantly enhance performance and user experience. Pre-rendering, using Suspense for SSR, and useOpaqueIdentifier are just some of the new features that can be beneficial when working with SSR.

In future versions of React, developers promise us new capabilities that will make our work even more efficient, simpler, and more organized. The impressive React ecosystem is constantly evolving, and exciting innovations await us.

Here are some of them:

1. Offscreen: This is a new API that will be introduced in future versions of React. It allows you to render components off-screen, which improves application performance and reduces page load time.
2. React Optimizing Compiler: This is a new tool that will be introduced in future versions of React. ROC allows you to optimize the performance of applications, speeding up the process of rendering components and reducing page loading time.
3. Asset Loading: In future versions of React, the handling of loading resources such as images, fonts, styles and other files will be improved. This will improve the performance and speed of applications, especially on mobile devices.
4. Server Components: A new model of working with server-side components that will increase speed and ease of use.
5. Transition Tracing: this is a new tool that will be introduced in future versions of React to simplify debugging and optimization of animations and transitions in the application. It allows developers to easily track and analyze the transition process between different states of components.

React remains at the forefront of web development, and these future possibilities will undoubtedly make our work with it even more enjoyable and productive.

Finally, I would like to say that React is constantly evolving and improving, and significant changes are expected in future versions. These changes can significantly improve the performance and responsiveness of React applications, and make React application development simpler and more efficient.