Why Is Debenhams Website So Slow? Here Are The Reasons

Debenhams is an online fashion retailer owned by Boohoo.com. The domain was previously owned by the British department store Debenhams.com and had entered liquidation. 

A speed report from Lighthouse paints a rather grim picture and scores Debenhams.com website 7.3 seconds on the speed index (SI), and 14% on Performance.

There are many reasons why the Debenhams website is so slow. This includes:

• Bloated JavaScript files
• Old Image formats
• Large DOM size
• Inefficient Scrolling Performance
• Ineffective Caching Policy

Let’s look at each of these reasons and identify potential ways that Debenhams can make their website load faster.

But before we do that, a quick word about our website CWVIQ.com - we are a free email alert service that sends out notification any time your website is loading very slowly (often due to heavy traffic, or poor scripts). If you have a website, consider setting up an alert so that you can fix issues before they become major. 

Bloated JavaScript files

Debenhams uses a lot of JavaScript to run the website. However, loading them all from one source could slow up the performance of the website. Debenhams can avoid this by splitting the code into smaller files. This way, you only load files that are necessary.

The Debenhams website can be as much as 3.15 seconds faster by adopting this technique.

Old Image formats

The Debenhams website uses a lot of JPG and PNG files that are considered outdated and heavy for modern web use. Replacing them with WebP and AVIF files can save as much as 0.90 seconds from the page loading time.

Large DOM size

The Debenhams website takes close to 11.5 seconds to evaluate all the scripts, parse them, compile, and render them. This can be minimized by minimizing the main-thread work. 

They may also look at reducing the number of nodes in the DOM. In simpler terms, you need to make sure that the main HTML code is smaller and has fewer nodes. I have explained this in greater detail in this article about DOMContentLoaded.

Inefficient Scrolling Performance

When you load Debenhams, you may notice a scroll jank – that is, the page stops responding to clicks and scrolls for a bit before catching up. This happens because the Debenhams website contains a bunch of JavaScript files with “active listeners” that prevent the browser from scrolling until they are completely loaded. This can be easily avoided by the use of passive listeners – just a small tweak to code that can make your page load more seamlessly.

Ineffective Caching Policy

A website like Debenhams is made of several components, including a lot of images, and other media files. Caching, or storing these components in your local computer, enables your browser to load the website much faster when you come back a second or third time. 

With Debenhams however, the cache for most media files clear is deleted every 30 minutes. This means that the website has loaded completely from scratch any time you visit after 30 minutes. Enabling a longer cache period could make loading pages faster and more user-friendly.