Best Practices for Web Page Loading Speed: Optimizing Reflow, Redraw, and Reflow

Improve web page loading speed: best practices for reflowing, redrawing and reflow, specific code examples are required

With the rapid development of the Internet, web page loading speed has It has become a crucial part of the user experience. No one wants to wait for long loading times, so how to improve web page loading speed has become a very critical issue.

The loading speed of web pages is affected by many factors, among which reflow, redraw and reflow are the three main performance bottlenecks. This article will introduce some best practices to help you optimize the loading speed of your web pages, and provide specific code examples.

1. Optimize HTML and CSS structure

The HTML and CSS structure of a web page is the basis for web page loading performance. Consider the following optimization options:

• Minimize the size of HTML and CSS files: remove unnecessary code, spaces and comments, and use compression tools to reduce file size.
• Reduce nesting levels: Too many nesting levels will cause the browser to repeatedly perform reflow and redraw operations, so try to keep the structure of HTML and CSS as flat as possible.
• Use external CSS files: Place CSS styles in external files to avoid inlining and duplication of styles.

2. Avoid triggering reflow and redraw

Reflow and redraw are two important factors that affect web page performance. They are usually triggered by changes to DOM elements, which often occur during user interaction or animation effects. Here are some ways to avoid triggering reflow and repaint:

• Use class instead of style attribute: Define the style as a CSS class instead of writing the style directly in the HTML element through the style attribute. This results in fewer modifications to the style, thus reducing the occurrence of redraws and reflows.
• Avoid frequent DOM operations: Reduce frequent addition, deletion, and modification operations on DOM elements, and try to complete multiple tasks in one operation.
• Use document fragments or offline DOM: Temporarily store DOM elements that require frequent operations in document fragments or offline DOM, and then add them to the page after completing the operation to reduce the number of reflows and redraws. .
• Use CSS animation instead of JavaScript animation: CSS animation can directly utilize the browser's hardware acceleration and is more efficient than animation implemented using JavaScript.

The following is a sample code to avoid frequent DOM operations:

<div id="container"></div>

<script>
  const container = document.getElementById('container');
  const fragment = document.createDocumentFragment();

  for (let i = 0; i < 1000; i++) {
    const listItem = document.createElement('li');
    listItem.textContent = 'List item ' + i;
    fragment.appendChild(listItem);
  }

  container.appendChild(fragment);
</script>

3. Preloading and lazy loading of content

Preloading and lazy loading are effective ways to optimize web page loading speed. Using preloading can load resources that may be needed in advance before the page is rendered, while lazy loading can load specific content when a certain condition is met.

The following is a sample code for preloading and lazy loading images:

<img src="/static/imghw/default1.png"  data-src="loading.gif"  class="lazy" data- alt="Image">

<script>
  const img = document.querySelector('img');
  const src = img.getAttribute('data-src');

  const image = new Image();
  image.onload = function() {
    img.setAttribute('src', src);
  };
  image.src = src;
</script>

In the above code, the preloaded image is first displayed as a loading animation, and then after the image resource is loaded , replace it with the actual image.

4. Merge and compress resource files

Merge and compress resource files can reduce the number of network requests and file size. Combine multiple CSS files or JavaScript files into a single file and use compression tools to reduce the file size. This reduces the number of round trips between the server and the browser and reduces file transfer time.

5. Use browser cache

Set the cache policy on the server so that the page can be obtained from the cache on subsequent loads instead of resending the request. By setting appropriate cache header information, the browser can cache static resources for a period of time, thereby reducing the load on the server and improving page loading speed.

The following is a sample code for setting up a cache on the Apache server:

<IfModule mod_expires.c>
  ExpiresActive on
  
  ExpiresDefault "access plus 2 weeks"
  
  <FilesMatch ".(png|jpg|jpeg|gif|ico|css|js)$">
    ExpiresDefault "access plus 1 month"
  </FilesMatch>
</IfModule>

This article introduces several best practices to improve web page loading speed, including optimizing HTML and CSS structures and avoiding triggering reflows and redraw, preload and lazy load content, merge and compress resource files, use browser cache, etc. I hope these technologies can help you improve the loading speed of web pages and provide a better user experience.

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