With the modern browsers came the inclusion of the navigation timing specification, allowing synthetic and real-user measurements to track more than the full completion by extracting this information via an API. The new information gave insight into each stage of a web page load by tracking Document Object Model (DOM) events, including the loadEventEnd, when a page theoretically becomes interactive to the user.
The problem with these metrics is that they are not indicative of the experience the user has. Many modern sites have asynchronous calls that occur after the loadEventEnd that are critical to the rendering and functionality of the page; or the loadEventEnd has to account for all the content that is still downloading and executing below the fold of the page. The question remains, when did the user perceive to have a completed page?
WebPageTest has introduced a new metric designed to address how quickly a page appears complete for an end-user, giving us a performance number for the time to render a page above the fold. User perception of speed is impacted by how quickly they see the content they are looking for. Based on an algorithm that looks at how the screen renders as measurements are taken, an AppDynamics Browser Synthetic monitor can report back the visually complete time for each page visited throughout a journey. Let’s look at an example comparing two retailers:
In this example, Retailer Two does a much better job of optimizing and presenting content to the end-user, gaining a performance edge over the competition. However, if we used the traditional synthetic metrics like loadEventEnd and Fully Loaded, we would erroneously think that Retailer Two was delivering a worse performance to their end-users and lagging behind the competition.
The browser synthetic tests afford us a deeper understanding of performance metrics, given we can directly observe the behavior of each page load as it happens, including when a user sees that their page has fully loaded. When using synthetic measurements as competitive benchmarks, it’s important to focus on the user-impacting metrics and not legacy numbers that may mislead about the experience of the end-user. The conversation needs to be moved from “fully loaded” and “time to loadEventEnd” to “What did the user actually experience above the fold?” To compare one site versus another, visually complete is the metric that truly reflects the end-user experience.