How should prefetch be exposed? about navigation-timing HOT 7 CLOSED

The first option seems fine to me. What's the navigationStart when prefetch is used?

from navigation-timing.

What's the navigationStart when prefetch is used?

It's still after the user clicks the link (or otherwise starts a navigation), in my view.

from navigation-timing.

I want to +1 to what Dan said in the WebPerfWG that resource timing seems to be a more appropriate place for this.

I assume we can't use existing timing attributes to implicitly expose whether a page is fetched? If not, then I wonder if another option could be to introduce a new timing attribute to do expose that implicitly?

from navigation-timing.

I assume we can't use existing timing attributes to implicitly expose whether a page is fetched? If not, then I wonder if another option could be to introduce a new timing attribute to do expose that implicitly?

I think it's possible. For sake of argument...

• Set NavigationType to prefetch
• Rest of variables are no different from cache or SW fetch case

Looking from the outside, a successful (adopted) prefetch looks the same to having a resource in memory / disk cache.

from navigation-timing.

Yoav and I will review the previous discussion and will present options in a future WebPerf WG call to move this forward.

from navigation-timing.

So it seems like we have multiple options here:

• Recognize that any resource can be prefetched, and hence add a "prefetch" indicator on PerformanceResourceTiming, as @DanShappir and @sefeng211 suggested.
• Add a "prefetch" indicator on PerformanceNavigationTiming, either as a stand alone boolean, or as part of the NavigationType enum
  • The latter would would mean that a prefetched navigation can't be any of the other types. We'd need to define e.g. what happens when a prefetched navigation is reloaded, etc.

I tend to agree that an indicator on the ResourceTiming entry (which NavigationTiming will inherit) may be a better fit. This seems related to w3c/resource-timing#303 as well as directly exposing if a resource was fetched from the cache (compared to today's jumping through hoops with transferSize that is required to get that info).

/cc @noamr

from navigation-timing.

Discussed on Apr 28 WebPerf WG call: https://w3c.github.io/web-performance/meetings/2022/2022-04-28/index.html

Summary:

• It seems fine to expose prefetch and Critical-CH signals orthogonally.

from navigation-timing.