Improving web page performance: What are some ways to reduce reflow and redraw costs?

Optimize page performance: How to reduce reflow and redraw overhead?

Optimizing page performance is an important consideration when developing web applications. Reflow and repaint are the two most expensive operations in the web page rendering process, and they consume a lot of computing resources and time. This article will introduce some methods and techniques to reduce the overhead of reflow and redraw, and improve the performance of web pages.

1. Use CSS3 animation
CSS3 provides some powerful animation features, such as animation and transition. Compared with animation effects implemented in JavaScript, CSS3 animations can more effectively reduce the overhead of reflow and redrawing. By using CSS3 animation, the animation effect can be implemented by the browser, reducing the execution frequency of JavaScript code, thereby optimizing page performance.

Sample code:

.element {
  transition: transform 0.3s ease-in-out;
}

.element:hover {
  transform: scale(1.2);
}

2. Avoid frequent DOM operations
DOM operations are one of the most expensive operations in the browser. Frequent operations on the DOM will cause a large number of reflows and redraws, resulting in reduced page performance. To reduce the frequency of DOM operations, multiple operations can be combined into one operation.

Sample code:

// 不推荐写法，频繁操作 DOM
const element = document.getElementById('element');
element.style.width = '100px';
element.style.height = '100px';
element.style.backgroundColor = 'red';

// 推荐写法，将多个操作合并为一个操作
const element = document.getElementById('element');
element.style.cssText = 'width: 100px; height: 100px; background-color: red;';

3. Use offline elements to perform operations
By placing operations in an offline element, you can minimize the impact on the page. Only when all operations are completed, the content of the offline element is inserted into the page, thereby reducing the number of reflows and redraws.

Sample code:

const fragment = document.createDocumentFragment();

for (let i = 0; i < 1000; i++) {
  const element = document.createElement('div');
  element.textContent = i;
  fragment.appendChild(element);
}

document.body.appendChild(fragment);

4. Use dynamic styles
By dynamically modifying styles, you can reduce the number of reflows and redraws. At the same time, concentrating styles in one place for modification can better manage and maintain the code.

Sample code:

const element = document.getElementById('element');
element.classList.add('highlight');

5. Use the tools provided by the browser for performance analysis
Modern browsers provide some developer tools, such as Chrome's developer tools and Firefox's flame Graphs can be used to analyze performance bottlenecks of web pages. By using these tools, developers can find the specific causes of reflows and redraws and optimize them.

Summary:
By reducing the overhead of reflow and redrawing, the performance of web pages can be greatly improved. During the development process, you should try to use CSS3 animations, avoid frequent DOM operations, use offline elements for operations, use dynamic styles, and use tools provided by the browser for performance analysis to optimize page performance. At the same time, reasonable code structure and good programming habits are also very important, which can improve development efficiency and reduce page rendering overhead.

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