Web Application Performance - Only ONE Aspect of Website User Experience
Test and Monitor | Posted March 07, 2012

What is the key to delivering great user experiences? Technical performance is only one part.

I have been pursuing the goal of trying to help customers measure, understand and optimize web application performance since 2000. One question I have been pondering for the last few years: what does “performance” mean exactly? 

Defining Technical Performance

Let's start by defining technical performance, which I define as a traditional fullpage or waterfall report that shows page load time for the overall page and every component of the page. This is the view of website performance that AlertSite and our contemporaries have provided for some time. It's also a view with which many may be familiar from Firebug or Webinspector or Webpagetest.org. While fullpage page load performance is valid and empirical, it does not address performance by way of user perceptions. 

And it's this “perceived” view of performance that is most important to User Experience. Have we all been doing it wrong all these years? Well… no, but to understand perceived performance we do need more sophisticated metrics. Fully understanding User Experience requires looking at performance through several lenses.

Fully Understanding User Experience

The first lens to perceive user experience consists of two events that the web browser itself provides while loading a web page: The DOMContentLoad and Page Load events.

The DOM Load fires when the browser has loaded the web page, but has not yet processed JavaScript or CSS files. This is typically the point at which the page becomes responsive to the user. The forms are accessible but perhaps the auto-correct or pre-fetch JavaScripts are not yet working when typing into the search form. A few colleagues whom I respect a great deal feel this Dom Load event is one of the most important timings to focus on related to user experience and I concur. A well-optimized web page will have a DOM Load event occur much earlier than a non-optimized page.  

The other event the browser provides is the Page Load event. This indicates the browser thinks the page and all its resources are completely loaded. It corresponds to time at which the browser would start executing JavaScript waiting for the onload event. 

DOM Load and Page Load - now part of AlertSite

The browsers perspective of user experience – DOM Load and Page Load – are now a part of AlertSite's web transaction monitoring. These new web application performance metrics are available to all customers and are visible today in AlertSite's detail reports. 

But we're not stopping there… 

How Long Does it Take to Load Pages Above the Fold

Several years back I met with an e-commerce manager from a significant retailer who allowed me to demonstrate our real browser web performance monitoring. While she acknowledged that our built-into-the-browser based record and playback technology was superior, she challenged me with something I have never forgotten.  She said, “While the fullpage page load data is important, what I care about most is how long it takes the page to load above the fold.” 

It seems to me that there are two observable events to a user’s perception: 1) When the page starts painting, and 2) when the page is loaded above the fold. I'll share the details with you later this summer, but suffice it to say that in the near future AlertSite's Web performance monitoring will be able to provide all of the data required to understand technical performance, user experience from the browser's perspective, and perceived user experience from the user’s perspective by capturing the above the fold page load times.


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