How to load images asynchronously in jquery

In front-end development, pictures are one of our commonly used contents. However, for some pages with a large number of pictures, loading them all at once may cause the page to respond slowly and reduce the user experience. Therefore, asynchronous loading technology needs to be used to optimize the page. performance. jQuery is an excellent JavaScript library that provides convenient methods to load images asynchronously.

The following will introduce how to load images asynchronously in jQuery.

1. Lazy loading of images

Lazy loading means loading images only when the user scrolls to the visible area. This technology can optimize page loading performance and improve user experience.

To implement lazy loading in jQuery, you can use the lazyload plug-in. This is a lightweight plug-in that does not require too much code. You only need to add the specified class to the image that needs to be loaded lazily, and then call the plug-in method.

The steps are as follows:

1. Download the lazyload plug-in and introduce the jQuery library.

2. Add the class attribute to images that need to be loaded lazily in HTML, as shown below:

<img class="lazyload" data-src="image.png">

3. Call the lazyload method in JavaScript and specify the class of the image that needs to be loaded lazily.

$(function(){
    $("img.lazyload").lazyload();
});

It should be noted that the real address of the image needs to be specified in the data-src attribute, not the src attribute. This way the original image address will not be loaded immediately, but will be loaded when needed.

2. Preload images

Preloading is to load the required images in advance. When needed, the cached images are used directly without making network requests. This technique can improve page display speed and user experience.

To preload images in jQuery, you can use the preload method. The code is as follows:

$.preload = function(){
    var args_len = arguments.length;
    for (var i = args_len; i--;) {
        $("<img>").attr("src", arguments[i]);
    }
}

This method receives multiple image addresses as parameters, and then uses jQuery to dynamically create img tags and specify the src attribute as Image address that needs to be preloaded. In this way, when these images need to be displayed, they can be taken directly from the local cache without making network requests.

This method can be called when the page is loading, for example:

$.preload("image1.png", "image2.png", "image3.png");

The effect of preloading images is not obvious, but it can effectively speed up image display when the network condition is poor.

3. Delayed loading of images

Delayed loading means asynchronously loading some required images after the page is loaded. This technology can avoid loading all the first-screen images, causing slow page loading.

To implement lazy loading in jQuery, you can combine the two technologies of lazy loading and preloading to achieve an effect similar to lazy loading.

It should be noted that delayed loading is less effective than lazy loading because it requires asynchronous loading of images after the page is loaded.

Summary

Asynchronous loading of images can effectively optimize page loading performance and improve user experience. To implement asynchronous loading of images in jQuery, you can use three technologies: lazy loading, preloading, and delayed loading. These technologies have their advantages in different scenarios.

Lazy loading can avoid loading too many images at once, causing slow page response, and improve page display speed and user experience. Preloading can improve image display speed and avoid waiting time caused by network requests. Delayed loading can combine the advantages of lazy loading and preloading, and load images asynchronously after the page is loaded to avoid slow page response caused by loading all the first-screen images.

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