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Optimize web page performance: reduce the impact of HTML reflow and redraw

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Release： 2024-01-26 08:29:05

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Optimize web page performance: reduce the impact of HTML reflow and redraw

Improve web page loading speed: How to reduce the impact of HTML reflow and redraw

With the rapid development of the Internet, web page loading speed has become one of the important indicators of user experience. one. One of the keys to improving web page loading speed is to reduce the impact of HTML reflow and repaint. This article will introduce how to improve the loading performance of web pages by optimizing code and using some techniques to reduce reflows and redraws.

1. What is HTML reflow and redraw

Reflow and redraw are two important processes that occur when the browser renders a web page.

Reflow refers to calculating which elements are displayed on the page based on the geometric properties and layout of DOM elements, and determining their position and size. When a reflow occurs, the browser recalculates and layouts the affected elements and then redraws the entire page.

Redrawing means that when the appearance attributes of a DOM element (such as color, border, etc.) change, the browser will apply the new appearance attributes to the element and redraw it without changing the layout of the element. and location.

The cost of reflow is much higher than that of redrawing, because reflow will cause the entire page to recalculate the layout, while redrawing will only change the appearance attributes of the element. Therefore, in order to improve the loading speed of web pages, we should try to reduce the number of reflows as much as possible.

2. Optimize style

Use class instead of style attribute: define the style uniformly in the CSS file, and change the style of the element by adding or removing class. This can reduce DOM operations and reduce the number of reflows.
Reduce the frequency of style changes: Combine multiple style modification operations into one. You can use CSS transform and transition properties to achieve animation effects, while also reducing the number of reflows.

3. Optimize JavaScript

Avoid frequent DOM operations:
a. Before modifying the DOM, you can save the DOM element to be modified in a variable, and then Modifications should be made to reduce the number of reflows.
b. Use document fragments (DocumentFragment) to perform batch operations on the DOM, and then add the document fragments to the DOM, which can also reduce the number of reflows.
Use CSS3 animation instead of JavaScript animation: CSS3 animation is based on GPU acceleration and is more efficient than JavaScript animation. You can use transition, transform, animation and other attributes to achieve animation effects.

4. Optimize layout

Use flexbox layout: Flexbox is a new layout method that can simplify web page layout operations and reduce the number of reflows.
Avoid using table layout: table layout will cause the entire table to recalculate the layout, so you should try to avoid using table layout, especially when the table content needs to be modified frequently.
Use event delegation: Bind the event listener to the parent element and capture the events of the child elements through event bubbling. This can reduce the number of event listeners and improve performance.

5. Other optimization techniques

Lazy loading: For some less important resources, you can delay loading them and load them only when the user needs to access them.
Image optimization: Compress image size and choose appropriate formats (such as JPEG, PNG) to reduce file size.
Use CDN acceleration: Placing the static resources (such as CSS and JavaScript files) required for web pages on CDN can speed up resource loading.

Code example:

<!DOCTYPE html>
<html>
<head>
    <style>
        /* 使用class代替style属性 */
        .hide {
            display: none;
        }
        .red {
            color: red;
        }
        .animate {
            transition: transform 0.3s ease;
        }
    </style>
</head>
<body>
    <!-- 使用CSS3动画代替JavaScript动画 -->
    <div id="box" class="animate"></div>

    <script>
        // 避免频繁操作DOM
        const box = document.getElementById('box');
        box.style.transform = 'translateX(100px)';
        box.style.transform = 'scale(0.5)';
    </script>
</body>
</html>

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By optimizing styles and JavaScript, as well as reasonable layout and other optimization techniques, we can reduce the impact of HTML reflow and redraw, thereby improving the loading of web pages speed. In actual development, we should choose appropriate optimization strategies according to specific situations to enhance user experience and improve web page loading performance.

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