How to solve page redraw and reflow issues and improve page performance

Optimize page performance: How to effectively solve the problem of page redrawing and reflow,
Require specific code examples

With the rapid development of the Internet, web pages have become One of the main platforms for people to obtain information and communicate. In daily use, we will inevitably encounter some problems such as slow page loading, freezing, flickering, etc. These problems are often related to page redrawing and reflow.

The so-called page redrawing means that when the style of an element of the page changes, the browser needs to redraw this element; while page reflow means that the page layout and geometric attributes change and need to be recalculated element's position and size, and then redraws the entire page. Redraw and reflow are important factors in browser performance bottlenecks, which can lead to slower page loading and reduced user experience.

In order to solve the problem of page redrawing and reflow, we can start from the following aspects:

1. Use transform to replace attributes such as top and left: when the position of the element changes, use Changing the transform attribute can avoid reflow. For example, we can change the position of the element through the following code:

// 不推荐
element.style.top = '100px';
element.style.left = '100px';

// 推荐
element.style.transform = 'translate(100px, 100px)';

2. Batch modification of styles: avoid frequently modifying the style of a single element, and try to concentrate the modifications of multiple styles together. For example, we can use class to modify the styles of multiple elements at once:

// 不推荐
element1.style.color = 'red';
element2.style.color = 'blue';
element3.style.color = 'green';

// 推荐
// CSS代码
/*
.red{
  color: red;
}
.blue{
  color: blue;
}
.green{
  color: green;
}
*/
// JavaScript代码
element1.classList.add('red');
element2.classList.add('blue');
element3.classList.add('green');

3. Use document fragments: When using JavaScript to dynamically generate DOM elements, we can use document fragments (DocumentFragment) to add elements in batches , rather than adding elements one at a time. This reduces the number of redraws and reflows.

// 不推荐
for(let i = 0; i < 1000; i++){
  let element = document.createElement('div');
  document.body.appendChild(element);
}

// 推荐
let fragment = document.createDocumentFragment();
for(let i = 0; i < 1000; i++){
  let element = document.createElement('div');
  fragment.appendChild(element);
}
document.body.appendChild(fragment);

4. Reasonable use of layout methods: avoid frequently changing layout methods, and try to use position attributes or flex layout and other methods to reduce the number of reflows. In addition, reflow will be triggered when using properties such as offsetWidth and offsetHeight. You should try to avoid using these properties too much.

In addition to the above methods, we can also use animation and transition effects in CSS3 to reduce the number of redraws and reflows, as well as use throttling and anti-shake technologies to control the triggering frequency of events and reduce duplication. redraw and reflow.

To sum up, optimizing page performance mainly includes avoiding unnecessary redrawing and reflow operations, and rationally using layout methods and related attributes. By optimizing these aspects, we can improve the loading speed of the page and improve the user experience.

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