Key Factors for Optimizing Web Page Performance: Relayout, Repaint, and Reflow

Reflow, redraw and reflow: key factors to improve web page performance

With the rapid development of the Internet, web page performance has become an important part of user experience. To improve web page performance, it is particularly important to understand and optimize the key factors in the web page rendering process. In the process of web page rendering, reflow, redraw and reflow are three key factors that directly affect performance. This article will analyze them in detail and explore optimization methods.

Reflow, also known as layout or reflow, refers to the browser determining the geometric properties of elements, such as position, size, etc., based on the box model. When the content of the web page changes, the browser will trigger a reflow operation to ensure that the elements are rendered in the correct order and position. However, reflow is a very expensive operation. It will cause the entire page to be re-layout, affecting the rendering of other elements, resulting in reduced page performance. Therefore, reducing reflow operations is an important task to improve web page performance.

Redrawing, also known as drawing, means that the browser draws an element based on its style information. Unlike reflow, redraw only affects the appearance of elements, not their layout. Although the redraw operation is faster than reordering, it still has a certain impact on performance. Therefore, reducing redraw operations is also one of the keys to optimizing web page performance.

Reflow refers to the process of combining the two operations of rearrangement and redrawing. When the content of the web page changes, the browser will first perform a reflow operation, and then perform a redraw operation to update the display of the page. Because the reflow operation involves page layout calculations, it is one of the most performance-impacting operations. In some cases, browsers force a reflow operation, resulting in poor performance. Therefore, reducing the number of reflows is one of the key strategies for optimizing web page performance.

To reduce the impact of reflow, redraw and reflow on web page performance, we must first understand the causes of these operations. Some common factors that cause reflowing and redrawing include changing the position, size, color, font and other attributes of elements, changing the size of the browser window, and triggering animation effects. Some common factors that cause reflow include changing the layout of elements, adding or removing elements, etc. Therefore, we can improve web page performance by avoiding these operations to reduce the number of reflows, redraws, and reflows.

In addition to avoiding the factors that cause these operations, some optimization strategies can also be adopted to reduce the number of reflows, redraws, and reflows. For example, you can use the CSS transform property instead of using top and left to change the position of an element, use the CSS opacity property instead of using background-color to change the color of an element, use requestAnimationFrame to optimize animation effects, etc. In addition, you can also use event delegation to reduce the number of DOM operations, use CSS Sprite to reduce the number of HTTP requests, and use cache appropriately. These strategies can effectively reduce the number of reflows, redraws and reflows of web pages, thereby improving the performance of web pages.

To sum up, reflow, redraw and reflow are key factors affecting web page performance. By understanding and optimizing these operations, we can improve the performance of web pages and provide a better user experience. Therefore, when designing and developing web pages, we should focus on reducing the number of reflows, redraws, and reflows, and adopt corresponding optimization strategies to improve web page performance.

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