Top level page metrics seems off when base URL is redirected

Whenever the base URL is redirected (for instance, being redirected to, some of the top-level data like _loadEventStart, _loadEventEnd, _domContentLoadedEventStart, _domContentLoadedEventEnd are all set to 0.

Is there a reason why it is the way it is and is there a work-around to get at the real values for the above metrics?


I’ll have to take a look but those numbers are just pulled from window.performance and there may be a restriction or something else going on becuase of the redirect to a SSL page.

Pat, thanks. I think it was my oversight. Turns out, I saw these numbers as 0 on IE-8/9 which doesn’t support nav-timing API altogether. On chrome and IE-10+, I do see these values being populated correctly even for redirected base pages.

Is there a work around to get these metrics for browsers that doesn’t support nav-timing API in another fashion from WPT?
For instance, _loadEventStart is very close to page.pageTimings.onLoad (or _loadTime).

loadEventStart should be the same as docTime (or Document Complete in the UI) which is often also exposed as the loadTime. The difference is that the loadEventStart is measured and reported by the browser while the doc time is measured by the code outside the browser. The biggest case where they will be different is with something like a javascript redirect where WPT will measure the full time but the browsers will only report the load time of the page after the redirect (because as far as they are concerned it is a different load).

While for loadEventEnd, there are other alternatives like you mentioned – _loadTime and _docTime, are there any work arounds for determining when the domContentLoaded event was fired? On browsers supporting nav-timing API, this is straightforward. But, for older browsers, like IE9 (or even safari), are there metrics in the HAR file that are close enough to the domContentLoadedEventStart?

I noticed that WPT itself skips showing the “DOM Content Loaded” strip if it is IE9 or below, but is there a close enough value that can be used in such cases?