Compare optimization strategies for reflow, redraw, and reflow to improve web page performance

Optimize web page performance: To discuss the advantages and disadvantages of reflow, redraw and reflow, specific code examples are needed

With the development of the Internet, web page performance optimization has become An important question that every front-end developer needs to face. In the process of optimizing web page performance, we need to understand and optimize for different operations. Among them, reflow, redraw and reflow are common problems that lead to reduced web page performance. This article will explore their advantages and disadvantages and give some specific code examples.

First of all, we need to understand the meaning of these three concepts:

1. Reflow: When the layout and geometric properties of DOM elements change, the browser needs to recalculate The element's geometric properties are then updated in its position on the page, a process called reflowing. Reflow is a relatively performance-intensive operation because it involves modifying and recalculating a large number of DOM elements.
2. Repaint: When the style attributes of a DOM element change but do not affect its geometric attributes, the browser will redraw the element. This process is called redrawing. Redrawing is relatively inexpensive because it only involves modifying style properties and updating the styles on the page.
3. Reflow (layout): Reflow is a combination of rearrangement and redrawing. When the layout, geometric attributes and style attributes of DOM elements change, the browser needs to recalculate the geometric attributes of the element and redraw the element. And update the position on the page, this process is called reflow.

Below we use several specific code examples to discuss the advantages and disadvantages of reflow, redraw and reflow.

Example 1:

// 重排
element.style.width = '100px';
element.style.height = '100px';
element.style.left = '10px';
element.style.top = '10px';

In the above code, we modified the layout and geometric properties of the element at the same time, which will trigger reflow and reflow. If we modify each property individually, we will reduce the number of reflows and reflows.

Example 2:

// 重绘
element.style.color = 'red';

In the above code, we only modified the style attribute of the element, which will trigger redrawing but not reflow and reflow. Therefore, the performance overhead of redrawing is small.

Example 3:

// 回流
element.style.width = '100px';
element.style.padding = '10px';
element.style.border = '1px solid red';

In the above code, we modified the layout, geometric properties and style properties of the element, which will trigger reflow. Similar to Example 1, in order to reduce the number of reflows, we can merge multiple modification operations.

To sum up, reflow, redraw and reflow will have a negative impact on the performance of the web page. In order to improve the performance of web pages, we can adopt some of the following optimization strategies:

1. Use the transform attribute of CSS instead of modifying the layout and geometric properties of elements, because transform will not trigger reflow and reflow.
2. When you need to modify the style attributes of an element multiple times, you can hide the element first, then modify it, and finally display it. This can reduce the number of reflows.
3. Use DocumentFragment or createDocumentFragment() method to perform DOM operations, and then add these operations to the document at once.
4. Avoid using table layout, because table layout will trigger a lot of reflow.

In short, optimizing web page performance is a comprehensive task. In the actual development process, we need to choose the appropriate optimization strategy according to the specific situation to improve the loading speed and user experience of the web page. At the same time, through the reasonable use of reflow, redraw and reflow techniques, we can reduce the number of these operations and thereby optimize the performance of the web page.

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