Asynchronous Loading of Third-Party Scripts with BARREL.asyncLoad

When building a website, performance is key. Loading too many third-party scripts can slow down your website, negatively affecting both user experience and SEO. One way to optimize your website’s performance is by loading third-party scripts asynchronously. In this post, we’ll explore how to use a custom JavaScript function called BARREL.asyncLoad to achieve this.

What is Asynchronous Loading?

Asynchronous loading means that your browser can continue loading other parts of your website while waiting for scripts to load. This prevents scripts from blocking your page’s content from rendering, which can significantly improve page speed.

Introduction to BARREL.asyncLoad

The BARREL.asyncLoad function is a custom JavaScript utility that allows you to load multiple external scripts asynchronously. This function is particularly useful if you want to include several third-party resources on your site without impacting its performance.

Here’s the complete code for BARREL.asyncLoad:

window.BARREL = window.BARREL || {};

window.BARREL.asyncLoad = function (urls) {
for (var i = 0; i < urls.length; i++) {
var s = document.createElement('script');
s.type = 'text/javascript';
s.defer = true; // Load script after HTML parsing is complete
s.src = urls[i].src; // URL of the script to load

// Optional: If a callback function is provided, execute it after the script loads
if (typeof urls[i].callback === 'function') {
s.addEventListener('load', urls[i].callback);
}

// Append the script to the page
var x = document.getElementsByTagName('script')[0];
x.parentNode.insertBefore(s, x);
}
};

How to Use BARREL.asyncLoad

You can use the BARREL.asyncLoad function to load multiple scripts by passing an array of objects. Each object should contain the script src URL, and optionally, a callback function that runs after the script has loaded.

Example Usage:

<script>
window.addEventListener('scroll', function () {
setTimeout(function () {
window.BARREL.asyncLoad([
{
src: 'https://apis.google.com/js/platform.js?onload=renderOptIn'
},
{
src: 'https://cdn.example.com/library.js',
callback: function () {
console.log('Library.js loaded successfully!');
}
},
{
src: 'https://analytics.example.com/tracker.js'
}
]);
}, 1000); // Delay loading by 1 second
}, { once: true });
</script>

Explanation

• Scroll Event Listener: In this example, the scripts are loaded only after the user starts scrolling. This can further optimize your page load by deferring non-critical scripts until user interaction.
• setTimeout: We add a slight delay (1000ms) before loading the scripts. This can help improve your page’s initial load speed.
• Script Loading:
  • The src property specifies the URL of the script to be loaded.
  • If a callback function is provided, it will execute after the script loads.

Use Cases

1. Loading Analytics Scripts: Defer loading analytics or tracking scripts until after the initial page load to reduce render-blocking.
2. Third-Party Widgets: If you’re using chat widgets or customer support tools, load them only after the user interacts with your page.
3. Performance Optimization: Great for lazy-loading scripts that are not essential for the initial rendering of your website.

Advantages of Using BARREL.asyncLoad

• Improved Page Load Time: By loading scripts asynchronously, you ensure they don’t block the rendering of your page.
• Reduced Render-Blocking: Deferred scripts do not block HTML parsing, improving your website’s speed score.
• Better User Experience: Faster load times lead to a better user experience and potentially higher conversion rates.

Best Practices

• Prioritize Critical Resources: Use this method only for non-critical scripts. Load essential scripts like core libraries (e.g., jQuery) using standard <script> tags with the defer attribute.
• Test Thoroughly: Ensure that any deferred scripts do not interfere with the functionality of your website.
• Monitor Performance: Use tools like Google Lighthouse, GTmetrix, or PageSpeed Insights to monitor the impact of async loading on your website’s performance.

Conclusion

Asynchronous loading of third-party scripts is a simple yet effective way to optimize your website’s performance. By using the BARREL.asyncLoad function, you can control when and how external resources are loaded, helping you build a faster and more responsive website.