In-depth study of key issues in page performance optimization: decryption, redrawing and reflow

Decrypting redrawing and reflow: in-depth exploration of key issues in page performance optimization

With the development of the network and the popularity of Internet applications, front-end performance optimization has become more and more important. an increasingly important issue. In the process of page performance optimization, two key issues are often encountered: redrawing and reflow. This article will delve into these two issues and provide specific code examples to solve them.

Redraw and reflow refer to the two key processes performed by the browser when rendering the page. Redrawing means that the browser will redraw the element when the style change does not affect its layout. Reflow means that when the size, position and other layout attributes of an element change, the browser needs to recalculate and re-render the entire page.

First, let’s explore the causes and solutions of redrawing. Redrawing is triggered when an element's style changes, even if the change has no effect on the layout. For example, when we modify the background color, font color, etc. of an element, redrawing will be triggered. Redrawing is usually caused by frequent changes to an element's style properties.

The solution to the redrawing problem can be from two aspects. First, we can combine style changes that trigger frequent redraws into a single operation. For example, we can use cssText or classList to modify multiple style attributes at once. This can effectively reduce the number of redraws.

Second, we can use the style class for optimization. When we need to change the styles of multiple elements, we can make batch modifications by changing the classes of the elements. This method can also reduce the number of redraws and improve page performance.

Next, we continue to delve into the issue of reflow. Reflow is the process of recalculation and rerendering due to changes to an element's layout properties. When we change the size, position and other attributes of the element, reflow will be triggered. Reflow is more expensive than redrawing because it involves relayout of the entire page.

To solve the reflow problem, we need to try to avoid frequently modifying the layout attributes of elements. First of all, we can use the transform attribute to replace top, left and other attributes, because transform will not trigger reflow. Second, we can use absolute positioning to adjust the position of an element instead of modifying its layout properties. Finally, we can also use document fragments (DocumentFragment) to insert elements in batches, thereby reducing the number of reflows.

In addition to the above methods, there are some other optimization techniques that can help us solve redraw and reflow problems. For example, we can use throttling and debounce to limit frequent style changes and layout attribute changes. We can also use slice rendering (requestAnimationFrame) to optimize the rendering process and reduce lags and performance issues.

The following is a specific code example that demonstrates how to reduce the number of redraws by merging modification operations:

// 不推荐的做法
const element = document.getElementById('myElement');
element.style.backgroundColor = 'red';
element.style.color = 'blue';
element.style.border = '1px solid black';

// 推荐的做法
const element = document.getElementById('myElement');
element.style.cssText = 'background-color: red; color: blue; border: 1px solid black;';

To summarize, during the page performance optimization process, we should pay attention to redraws and Impact of reflow on performance. By merging modification operations, using style classes, using transform attributes, and avoiding frequent changes to layout attributes, we can effectively reduce the number of redraws and reflows, and improve page performance and user experience.

By deeply understanding the causes and solutions of redraw and reflow, we can optimize page performance more effectively. I hope the content of this article can be helpful to readers and enable them to better solve related problems in front-end development.

The above is the detailed content of In-depth study of key issues in page performance optimization: decryption, redrawing and reflow. For more information, please follow other related articles on the PHP Chinese website!