Google lighthouse complains that the datepicker uses an eventlistener that is not passive

[martinfjant]

Describe the bug
Google lighthouse complains that the datepicker uses an eventlistener that is not passive

To Reproduce
Steps to reproduce the behavior:

1. Use the date picker somewhere
2. Run Google Lighthouse
3. Se warning

Expected behavior
Google lighthouse shows no warnings

Desktop (please complete the following information):

• Chrome, latest

Additional context
It might be related to ionic-team/stencil#2621

[WickyNilliams]

I've not been able to reproduce this. Can you give any more details?

[martinfjant]

I'm using the date picker twice on a page; I'm running Lighthouse on the latest Google Chrome on OSX Catilina.

[WickyNilliams]

Hmm we don't use any scroll listeners, so I'm surprised to see this - perhaps a browser extension is causing it?

I'm getting a pass for this on the demo/docs page https://duetds.github.io/date-picker/

[martinfjant]

It's actually not scroll, but touch listeners. It might not be anything within your control (I'm not very into how stencil works), but I do think it's related to ionic-team/stencil#2621 .

I've tested with all my addons disabled, and the results are the same. Touch start and touch end :(.

I might be able to make a minimal repo that resembles the one we have at work later!

[martinfjant]

Using lighthouse on the demo/docs gives me the same error as well.

[WickyNilliams]

So strange that I don't get it! Just to be sure there wasn't something weird going on with my own machine, I ran the test from the google site itself (https://web.dev/measure/) and got this result:

But we do use touch handlers. It may be possible to move to passive listeners, but i'm not 100% sure as we preventDefault() on touchmove

[martinfjant]

I ran that version on the code we're using and I do not get that error in the web.dev version! Do you use the same version of chrome? Nevertheless, if it's only my local Chrome that complains it won't affect a lot of other people! But it sure is an oddity.

[WickyNilliams]

Yes, I'm using that exact version of chrome. Very strange!

At least for now I will close this issue. In future I may look at adding lighthouse as an automated test of some sort, to prevent any perf regressions. Thanks for reporting