Ways to improve performance of reflow and redraw

How to optimize the performance of reflow and redraw requires specific code examples

Reflow and repaint are key concepts in web page performance optimization. Reflow refers to the process by which the browser calculates and re-renders the page layout, while redraw is the re-drawing of elements that already exist on the screen. These two processes have an important impact on web page performance, so optimizing the performance of reflow and redrawing is very important. This article will introduce some methods to optimize reflow and redraw, and give specific code examples.

1. Avoid frequent operation of style attributes

Frequent operation of style attributes will cause frequent reflow and redrawing. To avoid this, you can use CSS classes to style and then switch classes via JavaScript. This reduces the number of style changes, thereby reducing reflows and redraws.

// 不推荐的写法
document.getElementById('element').style.width = '100px';
document.getElementById('element').style.height = '100px';

// 推荐的写法
document.getElementById('element').classList.add('big-element');

2. Batch modification of style attributes

If you need to modify multiple style attributes at one time, you should try to put them in one code block instead of modifying them multiple times. This reduces the number of reflows and redraws.

// 不推荐的写法
document.getElementById('element').style.width = '100px';
document.getElementById('element').style.height = '100px';

// 推荐的写法
document.getElementById('element').style.cssText = 'width: 100px; height: 100px;';

3. Using CSS3 animations

CSS3 animations can take advantage of the browser's hardware acceleration, thereby reducing the overhead of reflow and redraw. Most modern browsers have optimized CSS3 animations, so their performance is better than JavaScript animations.

.element {
  transition: width 0.5s ease;
}

/* 通过 JavaScript 修改宽度 */
document.getElementById('element').style.width = '100px';

4. Use virtual DOM

Virtual DOM is an in-memory data structure that can efficiently perform calculations and comparisons, and then update the changed parts to the real DOM, thereby reducing the number of reflows and redraws.

Virtual DOM is often used with libraries or frameworks, here is a sample code using React:

// 不推荐的写法
ReactDOM.render(
  <div>
    <span>Hello</span>
    <span>World</span>
  </div>,
  document.getElementById('container')
);

// 推荐的写法
ReactDOM.render(
  <div>
    <span>Hello</span>
    <span>World</span>
  </div>,
  document.getElementById('container')
);

5. Using separate multi-layer layers

Separating different elements of the page onto independent layers can reduce the scope of reflow and redrawing. Use the transform or will-change attributes to improve rendering performance by placing elements into a separate layer.

/* 创建独立图层 */
.element {
  will-change: transform;
  /* 或者使用 transform 属性 */
  transform: translateZ(0);
}

In summary, performance optimization of reflow and redrawing is very important. By avoiding frequent manipulation of style attributes, batch modification of style attributes, using CSS3 animations, using virtual DOM, and using separate multi-layer layers, we can effectively reduce the number of reflows and redraws, thereby improving the performance and user experience of web pages. .

(This article only provides some common optimization methods and code examples. The actual optimization process needs to be comprehensively considered and adjusted according to the specific situation)

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