Optimizing web page rendering performance: detailed analysis of the mechanisms and countermeasures of redrawing and reflowing

Improve page rendering efficiency: in-depth analysis of the principles and prevention of redrawing and reflow

With the development of the Internet, the performance requirements of websites and applications are getting higher and higher. . Page loading speed has become one of the key factors of user experience. The improvement of page rendering efficiency can effectively reduce page loading time and improve user experience. In the process of optimizing page rendering efficiency, we need to understand and apply the principles of redrawing and reflow, as well as corresponding preventive measures.

First, let’s understand what redraw and reflow are. Redrawing means that when the style of an element changes, but does not affect its layout, the browser will redraw the appearance of the element. Reflow (also known as reflow or layout) means that when the DOM structure changes or the layout properties of an element change, the browser will recalculate the geometric properties of the element and then relayout the page.

Redrawing and reflow will consume a certain amount of time and resources, so we must minimize their occurrence to improve page rendering efficiency. Here are some common optimization suggestions:

1. Use appropriate CSS properties and selectors: Some CSS properties and selectors can cause reflow or redraw. Avoid using performance-impacting properties such as box-shadow and border-radius. Choose appropriate selectors and avoid using wildcards and sub-selectors as they increase selector weight and cause global backflow.
2. Avoid frequent DOM operations: DOM operations are very expensive and can cause reflows. Combining multiple DOM operations into a single operation and using document fragments (DocumentFragment) for batch insertion can reduce the number of reflows. In addition, try to avoid frequently modifying the style. You can change the style by adding or removing class names.
3. Use CSS3 animation instead of JavaScript animation: CSS3 animation is natively supported by the browser, uses GPU acceleration, and has higher performance than JavaScript animation. Use transform and opacity properties for animation effects to reduce redrawing and reflow.
4. Use virtual lists and lazy loading: When processing large amounts of data, split the list into a visible area and a non-visual area, and only render the contents of the visible area. Dynamically loading data while scrolling can reduce the load on the page.
5. Image optimization: Images are one of the important factors in web page loading time. Using appropriate image formats and reducing image size and quality can effectively reduce page loading time.
6. Reduce layout calculations: avoid frequently obtaining geometric attributes of elements, such as offsetTop and offsetWidth. In situations where you need to use it multiple times, save the result in a variable to avoid repeated calculations.
7. Use separated layout and style sheets: Place the style sheet at the head of the page and minimize inline styles. Place JavaScript code at the bottom of the page to avoid blocking the rendering of the page.
8. Use the browser's developer tools for performance analysis: Use the browser's developer tools to view the rendering performance of the page and identify performance bottlenecks. For example, Chrome's Performance tool can record and analyze page performance data.

By deeply understanding and applying the principles of redrawing and reflow, we can better optimize the rendering efficiency of the page. Try to avoid triggering frequent redraws and reflows, and optimize key rendering paths, which can greatly improve page loading speed and improve user experience. At the same time, we can also combine the browser's developer tools for performance analysis and optimization to obtain better page rendering effects.

Through the above optimization suggestions, we can effectively improve the page rendering efficiency, reduce the number of redraws and reflows, and thereby optimize the user experience. When developing websites and applications, we should focus on page performance optimization to provide a faster and smoother user experience.

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