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[Spike, 2hrs] Can we detect back button clicks after changing font
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On iOS 11, Chrome, perform the following steps on the new specialpages branch:

  • Visit article
  • Click settings cog in menu to visit Special:MobileOptions
  • Change font size to XL
  • Click back button

The font-size should switch from normal to XL on the back button

The font-size does not change.

To remedy this, we need to update the font size not only when the script is loaded but on some event. The question is which event?

Question to answer:

What JavaScript event mystery-event captures this scenario and allows us to do something like this?:

	function updateFontSize() {
		$( '#content p, .content p' ).css( 'font-size', userFontSize + '%' );
	$( window ).on( 'mystery-event', updateFontSize );

Developer notes

I had a quick look at using load and popstate events, neither of them seem to fire in this scenario. Which event can we use?

Event Timeline

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If the issue is to react to an event that gets triggered with the back button (and not pageLoad), we could use the pageShow event.
That might look something like this

$(window).on("pageshow", function(event) {
    if (event.originalEvent.persisted) {
        $( '#content p, .content p' ).css( 'font-size', userFontSize + '%' );

Jan yeh that sounds like it might work. Are you or anyone else able to investigate and verify whether that works for this particular scenario? If not I'll take a look tomorrow.

Change 405233 had a related patch set uploaded (by Jdlrobson; owner: Jdlrobson):
[mediawiki/extensions/MobileFrontend@specialpages] Update the font size on back button presses

I've confirmed this does the job and have submitted a patch.

Change 407047 had a related patch set uploaded (by Jdlrobson; owner: Jdlrobson):
[mediawiki/extensions/MobileFrontend@master] Update the font size on back button presses

Change 407047 abandoned by Jdlrobson:
Update the font size on back button presses

Change 405233 merged by jenkins-bot:
[mediawiki/extensions/MobileFrontend@specialpages] Update the font size on back button presses

Took a long look at Staging today and found that it seems to work well except in a few instances.

I am having troubles when switching from the large and x-large sizes to small. Here are some steps and a short video:


  1. Load an article
  2. Tap settings
  3. Change font to X-large
  4. Tap back and view the article
  5. Tap settings
  6. Change to Small
  7. Tap back and view the article

Font does not change

Note - It seems to happen most often going from X-large to small. I have occasionally seen it going from other sizes to small. The frequency is like 3/5.

I'm not sure if there's much more we can do here :/ Is it fair to say this is iOS specific?

Yes, I cannot repro this issue on android

I'm not sure if there's much more we can do here :/ Is it fair to say this is iOS specific?

do we know what might be causing this?

No i'm a bit lost now, as it seemed to be working when I was testing and we're now updating the font changer whenever the page is shown.

Will need more than 2hrs to investigate what's going on (maybe a day). Will need some real devices, the specific iOS version where it's happening and browser (either Chrome or iOS Safari).

Is this big enough of a problem to block the deploy?

Wouldn't consider it a blocker, but some more information would be helpful. @ABorbaWMF - would you mind looking through a number of devices and iOS versions (browsers? or are we sure that it's just Chrome)?

I've been able to reproduce the issue on following, but is not consistently happening:

iPhone X iOS 11 - Safari
iPhone 8 iOS 11 - Safari
iPhone 6s iOS 9 - Safari & Chrome & Firefox - Does NOT happen on UC Browser

I have not reproduced it on Android at all

Okay, looking into this this is looks like it's related to how the back-forward cache works and a bug in Safari.
There appears to be a potential fix but its labelled as a hack ( and after a bit of experimentation I cannot reliably get it to work :/ I would advise against trying this. Even if we can fix it on the short term there is no guarantee it will work in feature.
The same problem is what makes the menu stay open after you click the back button.

How do you want to handle this Olga?
It seems like a good option would be to avoid the user having to click back somehow... not sure if Nirzar has any good ideas there.

Resolving this. Let's open a separate bug for the other issue.