React, a popular JavaScript library for building user interfaces, has gone through several significant improvements since its inception. One of the most notable changes in recent versions of React is the introduction of a new rendering approach known as “concurrent rendering.” In this article, we will explore the traditional rendering process in React and how concurrent rendering brings about a fundamental shift in the way React updates the user interface.
Traditional React Rendering
In a traditional React application, rendering occurs in two distinct phases: the render phase and the commit phase. Let’s delve into these phases to understand how React updates the user interface.
The Render Phase
During the render phase, React performs a series of operations that involve comparing the current Document Object Model (DOM) with a newly generated “virtual DOM.” The virtual DOM is a lightweight, in-memory representation of the actual DOM. React calculates the differences between the current DOM and the new virtual DOM, preparing the necessary updates along the way.
The Commit Phase
Following the render phase is the commit phase. Here, React applies the updates calculated during the render phase to the actual DOM. This involves creating, updating, or deleting DOM nodes to match the new virtual DOM.
In a traditional synchronous render, React treats all elements within a component tree with the same level of priority. It executes rendering as a single, uninterruptible task, making sure that once rendering begins, it always finishes. However, this approach can lead to a potential drawback.
Synchronous rendering can become time-consuming, especially when dealing with complex components. During the rendering process, the main thread gets blocked, resulting in an unresponsive user interface until React completes the rendering and updates the DOM.
The Need for Concurrent Rendering
To address the issues associated with synchronous rendering, React 18 introduces a new rendering approach known as “concurrent rendering.” This new renderer operates in the background, offering ways to prioritize rendering tasks and make them more efficient.
Non-Urgent Rendering
One key feature of concurrent rendering is the ability to mark certain renders as non-urgent. When rendering low-priority components, React yields control back to the main thread at regular intervals, typically every 5 milliseconds. During these breaks, React checks for more important tasks, such as user input or high-priority component state updates. This allows React to prioritize essential tasks over less critical rendering operations.
In contrast to the all-or-nothing approach of synchronous rendering, the concurrent renderer makes rendering non-blocking by yielding control back to the main thread at regular intervals during the rendering of low-priority components.
Pausing and Resuming Rendering
The concurrent renderer takes the concept of pausing and resuming rendering to a new level. It can pause the rendering of one or multiple component trees based on external events, such as user interactions. For instance, if a user interacts with a specific component, React can pause the current rendering, prioritize the rendering of the interactive component, and then resume rendering the rest of the components. This ensures that React always focuses on what is most important for the user experience at any given moment.
Summary
In summary, the concurrent renderer brings a more flexible and responsive approach to rendering in React. It allows React to adapt to the priority of rendering tasks, making user interfaces more efficient and interactive. This improvement is especially valuable when dealing with large applications with complex component trees.
To see the benefits of concurrent rendering in action, you can explore the latest versions of React and take advantage of this powerful new feature. It promises to provide a smoother and more responsive user experience, making your React applications more robust and user-friendly.
So, as you embark on your journey with React, consider making the switch to concurrent rendering for a more dynamic and responsive user interface.
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