Rename and update semantics for navigation duration measurement #27
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This was referenced Feb 5, 2021
domenic
changed the title
yoavweiss
reviewed
Feb 17, 2021
| @@ -550,12 +550,14 @@ This can be useful for cleaning up any information in secondary stores, such as | |||
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| The `window.appHistory` object has an event, `currententrychange`, which allows the application to react to any updates to the `appHistory.currentEntry` property. This includes both navigations that change its value, and calls to `appHistory.updateCurrentEntry()` that change its `state` or `url` properties. This cannot be intercepted or canceled, as it occurs after the navigation has already happened; it's just an after-the-fact notification. | |||
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| This event has one special property, `event.navigationStartTimeStamp`, which for same-document navigations gives the value of `event.timeStamp` for the corresponding `navigate` event. This allows it to be used for determining the overall load time, including the time it took for a promise passed to `e.respondWith()` to settle: | |||
| This event has one special property, `event.startTime`, which for [same-document](#appendix-types-of-navigations) navigations gives the value of `performance.now()` when the navigation was initiated. This includes for navigations that were originally [cross-document](#appendix-types-of-navigations), like the user clicking on `<a href="https://example.com/another-page">`, but were transformed into same-document navigations by [navigation interception](#navigation-monitoring-and-interception). For completely cross-document navigations, `startTime` will be `null`. | |||
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s/includes for navigations/includes navigations/?
| _TODO: could we populate this for cross-document navigations too? Then it kind of overlaps with existing timing APIs, and is probably a lot harder to implement..._ | ||
| _TODO: reconsider cross-document navigations. There will only be one (the initial load of the page); should we even fire this event in that case? (That's [#31](https://github.com/WICG/app-history/issues/31).) Could we give `startTime` a useful value there, if we do?_ | ||
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| _TODO: is this property-on-the-event design the right one, or should we integrate with the performance timeline APIs, or...? Discuss in [#33](https://github.com/WICG/app-history/issues/33)._ |
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We should totally integrate this with the performance APIs, but that doesn't necessarily mean this timestamp is not needed. Are there other use cases for this timestamp, other than reporting?
e.g. I know that we have Event.timestamp, which is awfully similar.
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Closes #8 by renaming. Closes #12 by changing the semantics to when the navigation is initiated.
This might be refined further as we figure out navigation queuing.
/cc @esprehn @mmocny @yoavweiss @igrigorik
I do worry a bit about the name
navigationStart, as apparently in the navigation timing API definition, that is relative to the global monotonic clock, and not comparable to the values returned byevent.timeStampandperformance.now()? So I worry this is a misleading symmetry. WDYT?