To add loading animation to a web page, first create an animation structure and set the style with HTML and CSS, and then hide the animation after the page loading is completed through JavaScript. The specific steps are as follows: 1. Create an HTML structure for loading animations, such as a div containing a rotating icon; 2. Use CSS to set animation styles, including centered display, background color and animation effects; 3. Listen to the window.onload event through JavaScript, and hide the animation after the page resource is loaded; 4. You can combine the DOMContentLoaded event or imagesLoaded library to achieve more accurate load control; 5. Pay attention to avoiding animations hindering user interaction, adapt to mobile terminals and optimize page loading performance.

Adding loading animations or preloading pages to web pages is actually a very common need, especially on websites with a lot of pictures or content. Simply put, it is to display a prompt before the page is fully loaded, such as a rotated icon, progress bar, or animated effects such as brand logo. It is not difficult to implement, but there are several key points that need attention.

Basic structure and principle

To add a loading interface, the core idea is:

• When the page is just opened, the loading animation is displayed by default;
• After the page resources (HTML, CSS, JS, pictures, etc.) are loaded, hide this loading animation.

The implementation method is generally to use HTML CSS to make the animation part, and then remove or hide it after loading is completed.

 <!-- Basic structure of loading animation-->
<div id="preloader" class="preloader">
  <div class="spinner"></div>
</div>

Then hide it in window.onload :

 window.addEventListener('load', function () {
  document.getElementById('preloader').style.display = 'none';
});

How to design loading animation styles

Loading animations can be simple or fancy. Commonly, a small rotating circle or a progress bar with text. This part is mainly achieved by CSS.

To give a simple example, make a centered rotating circle:

 .preloader {
  position: fixed;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  background-color: #fff;
  display: flex;
  justify-content: center;
  align-items: center;
  z-index: 9999;
}

.spinner {
  border: 8px solid #f3f3f3;
  border-top: 8px solid #3498db;
  border-radius: 50%;
  width: 60px;
  height: 60px;
  animation: spin 1s linear infinite;
}

@keyframes spin {
  to { transform: rotate(360deg); }
}

You can change the color, size, position, etc. according to your website style. For example, if the dark background is replaced with a black background and a white animation.

More precise control of loading status

Sometimes you may want to not just hide the loading animation "the entire page is loaded", but control it more granularly, such as:

• The content will be displayed when the image is loaded partly;
• Or display the load status during the Ajax request.

At this time, you can consider combining the following methods:

• Use window.addEventListener('DOMContentLoaded', ...) to trigger hidden action in advance;
• Or manually control a variable and hide it after the key resources are loaded;
• If the page has a large number of images, you can use imagesLoaded libraries to monitor whether all images are loaded.

For example:

 document.addEventListener('DOMContentLoaded', function () {
  // The page DOM is loading, first hide the loading animation document.getElementById('preloader').style.display = 'none';
});

This allows users to see the content faster and improve the experience.

Notes and FAQs

• Don't let loading animations get stuck on page interaction : Make sure loading animations don't prevent users from clicking or scrolling.
• Mobile adaptation : The animation size and position must be displayed in the center on different devices.
• Loading time too long? That may be because the page resources are too large, so it is recommended to optimize pictures and compress JS/CSS.
• SEO and Accessibility : Loading animations themselves do not affect SEO, but search engines may lower the rating if the page is loaded for too long.

Basically that's it. Adding a loading animation is not complicated, but the details can make the user experience smoother.

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