[Responsiveness Metrics] - Select Elements

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Dave Smart

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Dec 20, 2021, 6:23:52 AM12/20/21
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Hi All,

Been having a play with the JavaScript Demos on https://web.dev/responsiveness/ & Hongbo Song's excellent article here: https://calendar.perfplanet.com/2021/hands-on-with-the-new-responsiveness-metrics/

This is perhaps me missing the point, but both show high latency for select elements on desktop, with a plain html select element recording latency of ~2-3 seconds (testing in chrome canary)

This doesn't occur in canary chrome on Android, which just records the click event, so I presume it's down to the human delay between pointer down and selecting an option? (If you use the keyboard to tab to the select and the arrow / enter keys, there's no issues).

Is this as intended? Is there some way we can account for this?




Nicolás Peña Moreno

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Dec 20, 2021, 9:10:30 AM12/20/21
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It is not intended for native select elements to have very long latencies. However I tried to reproduce this but couldn't. I think you are just clicking on the select elements and choosing options, right? Do you find consistent latencies of 2-3 seconds? Perhaps a screenshot of the console output would help. Also, which Chrome version are you using, and which OS?

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Dave Smart

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Dec 20, 2021, 9:21:59 AM12/20/21
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Hi, 

Not consistently 2-3 it seems, but consistently large:

select-latency.gif

That's chrome 99.0.4777.0 on Windows 10.

Nicolás Peña Moreno

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Dec 20, 2021, 6:16:06 PM12/20/21
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Thanks, it seems like a Windows problem. From a quick glance it looks like the issue are the event timestamps surfaced. The code snippets could be updated to ignore bogus (0 or negative) event timestamps, but I've also filed https://bugs.chromium.org/p/chromium/issues/detail?id=1281701 since we want this to work properly. Thanks for noting this problem!

Dave Smart

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Dec 21, 2021, 10:49:00 AM12/21/21
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Thanks for the info, and opening the bug report!

Dave Smart

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Mar 9, 2022, 1:54:05 PMMar 9
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Brilliant to see this metric rolling out to CrUX.

This particular issue still seems to be present on windows, (tried in Canary chrome) 

Is this just an issue in the JavaScript API or does it affect data sent to CrUX too?

Philip Walton

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Mar 9, 2022, 3:00:55 PMMar 9
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Thanks for pinging this thread, Dave.

I believe this issue just affects the JS API and not the data you see in CrUX. But the JS API is obviously very important as well, so we're going to prioritize getting this fixed.

Dave Smart

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Mar 9, 2022, 3:09:42 PMMar 9
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Thanks for the info, Philip!
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