Detailed explanation of how to dynamically load jQuery libraries using pure JavaScript. Since loading is done asynchronously, the callback version is included in the article so that you can understand when you can use jQuery after the script is inserted! I've posted an article about inserting scripts into a security page before, so you can find more options there.

Load jQuery library with pure JavaScript

// 使用純JavaScript加載jQuery庫
(function(){
  var newscript = document.createElement('script');
     newscript.type = 'text/javascript';
     newscript.async = true;
     newscript.src = 'https://ajax.googleapis.com/ajax/libs/jquery/1.6.1/jquery.min.js';
  (document.getElementsByTagName('head')[0]||document.getElementsByTagName('body')[0]).appendChild(newscript);
})();

Bring callback function version

(function () {

    function loadScript(url, callback) {

        var script = document.createElement("script")
        script.type = "text/javascript";

        if (script.readyState) { //IE
            script.onreadystatechange = function () {
                if (script.readyState == "loaded" || script.readyState == "complete") {
                    script.onreadystatechange = null;
                    callback();
                }
            };
        } else { //其他瀏覽器
            script.onload = function () {
                callback();
            };
        }

        script.src = url;
        document.getElementsByTagName("head")[0].appendChild(script);
    }

    loadScript("https://ajax.googleapis.com/ajax/libs/jquery/1.6.1/jquery.min.js", function () {

         //jQuery 加載完成
         console.log('jquery loaded');

    });


})();

FAQs on dynamic loading of jQuery libraries in JavaScript

Why do you need to dynamically load jQuery library in JavaScript?

Dynamically loading jQuery in JavaScript is a technique that only loads jQuery libraries when needed. This can significantly improve web page performance by reducing initial load time. When the page loads, all scripts linked in the HTML file are loaded as well. If you don't need to use jQuery right away, dynamic loading it saves bandwidth and speeds up page loading. This technique is especially useful for websites that use jQuery only for specific features rather than for the entire website.

How does dynamic loading of jQuery work?

Dynamic loading of jQuery involves using JavaScript to load the jQuery library only when needed. This is done by creating a new script element, setting its source to the jQuery library URL, and then appending this script element to the HTML document. Once the script is attached, the browser will get the jQuery library and execute it. This process is usually done within a function that can be called when jQuery is needed.

Can I use the jQuery function immediately after dynamically loading jQuery?

No, you cannot use the jQuery function immediately after dynamically loading jQuery. This is because the browser loads the script asynchronously. This means that the script continues to load in the background while the rest of your code is being executed. So you need to make sure that jQuery is fully loaded before you start using it. This can be done by using a callback function executed after jQuery is loaded.

How to make sure jQuery is loaded before using jQuery?

You can make sure that jQuery is loaded before using jQuery by using callback functions. A callback function is a function that is passed as an argument to another function and executed after another function is executed. In the case of dynamic loading of jQuery, you can pass the callback function to the function that loads jQuery. This callback function will contain all jQuery code and execute after jQuery is fully loaded.

What are the benefits of dynamically loading jQuery?

Dynamic loading of jQuery has many benefits. First, it can significantly improve the performance of the website by reducing the initial load time. This is because the jQuery library is only loaded when needed, not with the rest of the HTML documents. Secondly, it can save bandwidth, especially for users with slower Internet connections. Finally, it can make your code more modular and easier to maintain, as you can load jQuery only for the part of the website that needs it.

Is there any disadvantages of dynamic loading jQuery?

One potential drawback of dynamically loading jQuery is that it will make your code more complicated. This is because you need to make sure that jQuery is fully loaded before you start using jQuery, which usually involves using callback functions. However, the benefits of improved performance and reduced bandwidth usage often outweigh this disadvantage.

Can I load other JavaScript libraries dynamically like jQuery?

Yes, you can dynamically load other JavaScript libraries like jQuery. The process is the same: Create a new script element, set its source to the URL of the library, and append it to the HTML document. This technique can be used in any JavaScript library, not just jQuery.

Can I dynamically load multiple versions of jQuery?

Yes, you can dynamically load multiple versions of jQuery. However, you need to be careful to avoid conflicts between different versions. jQuery provides a function called noConflict() that can be used to avoid such conflicts. This function returns control of the $ variable to the first library that implements it, allowing multiple versions of jQuery to coexist.

Can I use dynamically loaded jQuery with other JavaScript libraries?

Yes, you can use dynamically loaded jQuery with other JavaScript libraries. However, you need to make sure jQuery is fully loaded before you start using it with other libraries. This can be done by using a callback function executed after jQuery is loaded.

Is dynamic loading jQuery compatible with all browsers?

Dynamic loading jQuery is compatible with all modern browsers that support JavaScript. However, for very old browsers that do not support dynamic script loading, you may want to include jQuery in the HTML document in a traditional way.

The above is the detailed content of Dynamically Load jQuery Library Using Plain JavaScript. For more information, please follow other related articles on the PHP Chinese website!