A website's loading speed is critical to both user experience and search engine optimization. One of the most important techniques that can improve loading speed is to optimize the loading of JavaScript, using the techniques delay and defer.

In this article, we'll break down these two techniques, explain how they work, and consider which method is preferable for optimizing the loading of a website using WordPress.

When a web page loads, the browser performs a series of actions to make the content available to the user. One of the most important parts of this process is loading and executing the JavaScript files.

What do the terms delay & defer mean?

• Delay: The delay technique involves delaying the loading of a script until a specific event occurs, such as the completion of page loading or a user action. This means that the script does not load immediately with the rest of the content, but at a delayed time.

• Defer: defer is a command added to the tag και επιτρέπει στον φυλλομετρητή να φορτώσει το script ταυτόχρονα με το υπόλοιπο περιεχόμενο της σελίδας, αλλά να το εκτελέσει μόνο αφού έχει ολοκληρωθεί η φόρτωση του DOM (Document Object Model). Αυτό διασφαλίζει ότι η JavaScript δεν θα παρεμποδίσει την αρχική απόδοση της σελίδας.

How the Javascript delay or deferral process works

1. Defer: When you use the defer parameter, the script is loaded in the background while the rest of the page content is loaded and rendered to the user. When the page is fully loaded, then and only then is the script executed. This helps minimize page rendering lag.

<script src="example.js" defer></script>

2. Delay: To delay a script, a timer (timeout) or a listener can be used in an event. For example, you might delay loading the script until the page has finished loading or until the user takes an action.

<script>
  window.onload = function() {
    // Καθυστέρηση φόρτωσης script έως την ολοκλήρωση φόρτωσης της σελίδας
    var script = document.createElement('script');
    script.src = "example.js";
    document.body.appendChild(script);
  }
</script>

Which method is preferable?

The choice between defer and delay depends on the needs of your website and how you want to optimize the user experience.

• Defer: is the most common and preferred method for the majority of cases. It allows parallel loading of the script without interrupting the page load and ensures that the JavaScript will only be executed when the DOM is fully ready. This technique is ideal for scripts that do not affect the original appearance of the content.

• Delay: can be useful for scripts that are not critical for the initial page load, such as analytics or ads. In these cases, delaying the loading of these scripts until the user interacts with the page can reduce load time and improve the user experience.

Advantages

• Faster Performance: Using defer ensures that the content of the page will be displayed faster to the user, since the loading of the JavaScript files does not block the rendering of the content.

• Better SEO performance: Search engines, such as Google, evaluate the loading speed of the web page for ranking in the search results. By using defer or delay, you can reduce page load time, thus improving your SEO performance.

• Reduced Resource Consumption: By delaying the loading of non-critical scripts with delay, you can reduce resource consumption, especially on mobile devices, improving the user experience.

Hands-on WordPress implementation

In WordPress, JavaScript loading optimization can be achieved by using appropriate plugins. Some popular options are:

• WP Rocket: Offers features for using defer and optimizing JavaScript loading.

• Autooptimize: A free plugin that allows the use of defer and delay to improve website loading speed.

• Async JavaScript: This plugin allows you to load JavaScript files asynchronously or use defer.

Incorporating these methods can significantly improve your website's loading speed, ensuring a more pleasant experience for visitors and better search engine performance.

Conclusion

Optimizing the loading of JavaScript through defer and delay techniques is an important step in making a web page load faster. Choosing the appropriate method depends on the needs of your website, but using defer is usually the most preferred approach. With the right implementation in WordPress, you can significantly improve the performance of your website, providing a better experience to your users and strengthening your SEO strategy.