Improving web page performance: Tips to reduce reflows and redraws

Optimizing web page performance: How to reduce reflows and redraws

Abstract: In web development, optimizing performance is crucial. Among them, reducing reflow and repaint is a key factor in improving web page performance. This article will introduce the principles of reflow and redrawing in detail, and give specific code examples to help developers reduce reflow and redrawing and improve web page performance.

1. Principles of reflow and redraw

Reflow refers to the process in which the browser recalculates the geometric properties of the element when the geometric properties of the DOM element change, and then re-lays out the entire page. Redrawing is the process by which the browser redraws an element when its style changes.

The cost of reflow is relatively high, which will cause the browser to recalculate the layout and redraw the page, thus affecting the performance of the page. Therefore, reducing reflow is a key optimization point.

2. Methods to reduce reflow and redraw

1. Use the browser's developer tools to detect reflow and redraw

Modern browsers provide With the developer tools, reflow and redraw can be easily detected. During the development process, these tools can be used to locate performance problems and optimize them.

2. Avoid frequent reading and writing of style attributes

In JavaScript, frequent reading and writing of style attributes will cause reflow and redrawing. In order to reduce reflow and redrawing, frequent reading and writing of style attributes should be avoided as much as possible. You can reduce the reading and writing of style attributes by adding a class name to an element and then modifying the element's style at once.

For example, the following code will cause multiple reflows and redraws:

const element = document.getElementById('element');
element.style.width = '100px';
element.style.height = '200px';
element.style.backgroundColor = 'red';

while the following code will only trigger one reflow and redraw:

const element = document.getElementById('element');
element.classList.add('custom-style');

3. Use CSS3 animations instead of JavaScript animations

Using CSS3 animations in web pages can improve the performance of animations, because CSS3 animations are executed in the browser's UI thread, while JavaScript animations are executed in the JavaScript thread. Yes, if the animation frequency is too high, it will cause the JavaScript thread to block, thus affecting the performance of the page.

4. Use the virtual DOM library

Virtual DOM is a JavaScript object that uses JavaScript objects to represent the structure and properties of the real DOM, and by comparing the differences between the virtual DOM and the real DOM. Techniques for minimal reflow and repaint. Using a virtual DOM library can effectively reduce the number of reflows and redraws, thereby improving page performance.

5. Use requestAnimationFrame for animation

When developing animation effects, you should try to use requestAnimationFrame instead of setTimeout or setInterval. requestAnimationFrame is an API provided by the browser, which can optimize the performance of animation and avoid frequent reflow and redrawing.

3. Code Example

The following is a code example that uses requestAnimationFrame for animation:

function animate() {
  const element = document.getElementById('element');
  let position = 0;
  
  function update() {
    position += 1;
    element.style.left = position + 'px';
    
    if (position < 100) {
      requestAnimationFrame(update);
    }
  }
  
  requestAnimationFrame(update);
}

This code will move an element on the page, each time it moves a distance is 1 pixel until the element moves to a position 100 pixels from the left.

Summary:

In web development, optimizing performance is very important. Reducing reflows and redraws is a key factor in improving web page performance. By using the browser's developer tools to detect reflows and redraws, avoiding frequent reading and writing of style attributes, using CSS3 animations instead of JavaScript animations, using virtual DOM libraries, and using requestAnimationFrame for animations, reflows and redraws can be effectively reduced. , improve the performance of web pages. We hope that the code examples in this article can help developers better optimize web page performance and improve user experience.

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