Tips to speed up web page loading: rearrange, redraw and reflow

Reflow, redraw and reflow: the secret to optimizing web page loading speed

In today's mobile Internet era, the loading speed of web pages is crucial to user experience. A slow-loading web page annoys users and may cause them to abandon their visit. Therefore, optimizing web page loading speed has become one of the important tasks in web design and development.

When optimizing web page loading speed, we often encounter terms such as reflow, redraw and reflow. Understanding the meaning of these terms and how to avoid their impact on web page performance will help us better optimize web page loading speed.

First, let’s understand reflow: When the layout and geometric properties of the page change, the browser needs to recalculate the layout of the elements. This process is called reflow. For example, when we change the position, size or display state of an element, reflow will be triggered.

Repaint means that when the appearance attributes of the page change, the browser needs to redraw these elements to present a new style. Redrawing does not involve changes to the layout, but simply changes the appearance of the element.

Reflow (layout) is a comprehensive process of rearrangement and redrawing. When the layout or geometric properties of the page change, the browser will perform a reflow operation, calculate the layout of the elements, and redraw the elements based on the new layout results.

So, why do reflow, redraw and reflow affect the loading speed of web pages? There are two main reasons for this. First, reflow and reflow consume a lot of computing resources, especially when the number of elements is large or the page is complex. Secondly, reflow and reflow will cause the page content to be re-rendered, which will increase the workload of the browser and thereby extend the loading time of the web page.

So, how should we avoid or reduce the occurrence of reflow, redraw and reflow, so as to improve the loading speed of web pages? Here are some methods and tips:

1. Use CSS animations instead of JavaScript animations: CSS animations use GPU acceleration, while JavaScript animations trigger reflows and reflows. Therefore, using CSS animation as much as possible to achieve dynamic effects on web pages can effectively reduce performance losses.
2. Avoid frequent style changes: Since style changes will trigger reflow and redraw, frequently modifying the style of elements will increase the loading time of the web page. Consider combining multiple style changes into a single operation, or using CSS classes to modify styles in batches.
3. Concentrate DOM operations: DOM operations will also trigger rearrangement and redrawing. Minimize the number of DOM operations and merge multiple operations into one.
4. Use CSS3 animation effects: CSS3 provides some hardware-accelerated properties, such as transform and opacity. Animation effects using these properties enable the browser to perform GPU acceleration and reduce the number of reflows and redraws.
5. Avoid table layout and floating layout: Table layout and floating layout will trigger reflow and reflow, try to use flexbox layout or grid layout instead.

When optimizing web page loading speed, we can also use some tools and techniques to help us analyze and optimize page performance. For example, use the Chrome Developer Tools Performance panel to view performance metrics and timelines at various stages in the page load process to find performance bottlenecks.

In short, reflow, redraw and reflow are important factors that affect the loading speed of web pages. By understanding these concepts and taking corresponding optimization measures, we can effectively improve the loading speed of web pages and provide a better user experience.

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