Re: [NavigationTiming] a couple questions

On Wed, Nov 10, 2010 at 8:32 AM, Tony Gentilcore <> wrote:
> We discussed naming/location on a previous call. IIRC, here were the
> points we came to (others please keep me honest here):
> - Hang it under console? The goal of the performance object is to
> expose information to the DOM in production. This is distinct from
> console which only interacts with the debugging console during
> development.

The console object is available to DOMs in production too.

> - Hang it under document? There are subtle differences between window
> and document lifetimes (for instance a late document.write can replace
> the document). The performance information outlasts a document, so it
> didn't make a whole lot of sense there. However, I don't recall any
> strong objections to moving it if we want to revisit.

document.write doesn't replace the document, it just replaces the
contents (elements, textnodes, etc) of it.

> - Will global performance conflict with many sites?

Your guess is as good as mine. There's a lot of sites out there
though, chances are good that many use variables with such a name.

> We discussed
> allowing it to be replaceable so that if a site were to define var
> performance or window.performance, it would override the built-in.
> This would mitigate all but the most pathological conflicts.

Most, but not code that tests if a variable is there, or checks if
it's true/false. I.e. code like

if (!performance) {
  performance = calculatePerfMetrics();

> Unfortunately, I don't recall where we ended up on this discussion and
> can't find anything one way or the other in the spec.
> Another alternative which I don't think we discussed would be to hang
> them directly under navigator. e.g. navigator.timing,
> navigator.navigation...

The navigator object is tricky since its lifetime is actually longer
than that of the page. It survives from one page to the next within
the same origin at least in gecko.

/ Jonas

Received on Wednesday, 10 November 2010 17:00:26 UTC