Key measures to optimize web page performance: decryption redraw and reflow

Decrypting Redraw and Reflow: Key Steps to Optimize Web Page Performance

In today’s Internet era, fast loading and smooth user experience are the priorities of every web designer and The goals that developers pursue. However, we often encounter problems with slow loading of web pages or page freezes. Some of these problems are caused by the browser redrawing and reflowing the page. Understanding how redraw and reflow work, and taking corresponding optimization measures, can significantly improve the performance and responsiveness of your web pages.

First, let us understand the definitions of redraw and reflow. When the style of an element on the page changes, the browser will recalculate the element's geometric properties (such as position and size) and redraw the element based on the new property values. This process is called reflow. Repaint refers to updating the drawing of elements without changing the geometric properties of the elements, and is completed by updating the display content.

Although redrawing and reflowing are necessary steps in the browser, frequent redrawing and reflowing will greatly affect the performance of the web page. This is because redrawing and reflowing are computationally intensive operations that require the browser to spend considerable time and resources to complete. Repeatedly performing these operations will cause page delays and freezes.

So, how should we optimize web pages to reduce redraws and reflows?

The first step is to try to avoid frequent style changes. Changing the style of the same element multiple times will cause multiple reflows and repaints. Therefore, we can consider using CSS class selectors to change the styles of multiple elements at once, or put elements that require frequent style changes in a separate layer, which will only cause the layer to be redrawn and reflowed.

The second step is to use CSS animations instead of JavaScript animations. Using CSS animations can take advantage of the browser's hardware acceleration features, thereby reducing the number of reflows and redraws. In contrast, animations implemented in JavaScript are more likely to cause frequent reflows and redraws.

The third step is to use event delegation appropriately. Event delegation refers to binding the event handler to the parent element and processing the events of the child elements through the event bubbling mechanism. The advantage of this is that it reduces the number of event handlers and thus the number of reflows. In contrast, binding event handlers to each child element would result in excessive reflows and redraws.

The fourth step is to use caching to reduce repeated calculations. Some calculations are repeated, such as getting the position and size of an element. Using a cache to store the results of these calculations avoids repeated calculations, thereby reducing the number of reflows.

Finally, we need to perform performance testing and optimization. Using some browser developer tools, such as Chrome developer tools, can help us analyze the loading and rendering performance of web pages and find performance bottlenecks. Based on the test results, gradually optimize and adjust the style and structure of the web page to improve the performance and user experience of the web page.

To sum up, understanding the mechanisms of redrawing and reflow and taking corresponding optimization measures are key steps in optimizing web page performance. By optimizing style changes, using CSS animations, rationally using event delegation, utilizing caching, and performing performance testing and optimization, we can reduce performance problems caused by redrawing and reflowing, and improve the loading speed and user experience of web pages. In the process of web design and development, we should always pay attention to web page performance and constantly pursue the possibility of optimization.

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