In-depth understanding of reflow and redraw: basic understanding of improving web page performance

Understand reflow and redraw: the basics of optimizing web page performance

With the rapid development of the Internet, web page performance optimization has become more and more important. In terms of user experience, the loading speed and response time of web pages are crucial. Reflow and repaint are two key factors that affect web page performance. This article will introduce the concepts of reflow and repaint, and how to optimize web page performance.

Reflow refers to the process when the browser rendering engine calculates layout information. It recalculates the geometric properties of the element and recalculates the position and size of the element. Reflow is a very resource-intensive operation that requires the entire page layout to be recalculated and triggers the re-rendering of other elements. Therefore, the more frequent reflows occur, the worse the page performance will be.

Redrawing refers to the process in which the browser rendering engine will redraw the element based on the new style information when the appearance of the element changes. Redrawing does not involve changing the position or size of elements, so it is lighter-weight than reflowing. However, if the frequency of redrawing is too high, it will still have a negative impact on the performance of the web page.

So, how to reduce the impact of reflow and redraw on web page performance? The following are some commonly used optimization methods:

1. Use CSS Transitions and Animations: Try to use CSS animations to achieve dynamic effects, because CSS animations can enable the browser to use hardware acceleration and reduce the frequency of reflow and redrawing. .
2. Avoid frequent DOM operations: DOM operations are very resource-intensive, so try to reduce the number of DOM operations as much as possible. Multiple DOM operations can be combined into one operation, or document fragments can be used to perform batch operations.
3. Use offline rendering technology: Offline rendering technology can render elements first and then display them on the page, reducing the number of reflows and redraws. For example, dynamic content can be rendered using canvas, and then the rendered canvas can be displayed on the page.
4. Avoid frequent style modifications: Try to avoid frequently modifying the style of elements, because each style modification will cause reflow and redrawing. You can modify styles in batches by adding classes, or use CSS animation to achieve dynamic effects.
5. Use positioning layout and cached layout information: Try to use positioning layout (position:absolute or position:fixed) and cached layout information to reduce the number of times the browser recalculates the layout.
6. Reduce the resource loading of the page: Reducing the resource loading of the page can speed up the loading speed of the web page, thereby reducing the number of reflows and redraws. Can merge and compress CSS and JavaScript files, optimize image size, etc.

By understanding the principles of reflow and redrawing and taking corresponding optimization measures, you can effectively improve the performance and user experience of web pages. Optimizing web page performance is an iterative process that requires ongoing attention and improvement. I hope the basic knowledge provided in this article will be helpful to you in optimizing web page performance.

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