Methodology

How does Boomerang work?

1. Measuring Navigations

We define Page Load Time (PLT) or Round Trip Time (RTT) as the time taken from the user initiating a navigation to when that page is completely available for the user to interact with.

Modern browsers support the NavigationTiming API, which provides high-resolution timestamps for each stage of the navigation. Boomerang uses the NavigationTiming API when available to measure Page Load performance.

In older browsers that do not support the NavigationTiming API, Boomerang is able to measure inter-site navigations by calculating the difference between when the old page is about to be unloaded (onbeforeunload) to when the new page is loaded (onload).

This is how Boomerang measures Page Load in older browsers:

• On the current page (before the navigation), attach a callback to the window.onbeforeunload event.
  • When onbeforeunload fires, log the timestamp and store it into a session cookie along with the URL of the current page.
• On the new page, attach a function to the window.onload event.
  • When onload fires, log the timestamp.
  • Look for the cookie where we set the start time and referrer
  • Check the URL stored in the cookie with the document.referrer of the current document. If these two differ, it means that the user possibly visited a third party page in between the two pages from our site and the measurement is invalid, so we abort.
  • If the above rules pass, we pull the time out of the cookie and remove the cookie. We measure the difference in the two times and this is the Page Load time for the current page.

Note that in browsers that do not support NavigationTiming, Boomerang is unable to measure the Page Load time of the first navigation to a domain, since it is not running on the referrer page. For example, if a visitor comes from a search engine, the total Page Load time cannot be determined.

2. Measuring XMLHttpRequests

See BOOMR.plugins.AutoXHR for more details.

3. Measuring Single Page Apps

See BOOMR.plugins.SPA for more details.

4. Measuring Bandwidth & Latency

See BOOMR.plugins.BW for more details.

5. Measuring DNS

See BOOMR.plugins.DNS for more details.

6. Measuring Waterfall

See BOOMR.plugins.ResourceTiming for more details.

6. Measuring Other Arbitrary Events

See Measuring arbitrary events for more details.