[wp-trac] [WordPress Trac] #52758: 5.7 About Page: Image comparison doesn't work on first load on some browsers

[WordPress Trac]

#52758: 5.7 About Page: Image comparison doesn't work on first load on some
browsers
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 Reporter:  vladytimy     |      Owner:  (none)
     Type:  defect (bug)  |     Status:  new
 Priority:  normal        |  Milestone:  Awaiting Review
Component:  Help/About    |    Version:  5.7
 Severity:  normal        |   Keywords:
  Focuses:                |
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 The image comparison script doesn't work **on the first load of the page**
 (after updating) - on some browsers. It works if page is refreshed.

 First mentioned
 [https://wordpress.slack.com/archives/C02RQBWTW/p1615330959309800 here] by
 @joyously

 The [https://youtu.be/JVRXEU-mPkA video showing the issue]

 == The updating scenarios explored on Chrome & Edge

 - 5.6.2 => 5.7 ==> Doesn't work
 - 5.6.2 => 5.7 => 5.6.2 (rollback) => 5.7 ( all in the same browser) ==>
 Works!
 - 5.6.2 => 5.7 => 5.6.2 (in browser A) & 5.6.2 => 5.7 (browser B) ==>
 Doesn't work!
 - Fresh install of 5.7 (both local & on a server) /wp-admin/about.php ==>
 Works!

 And now a strange thing (I'll accept if this can't be replicated, since I
 don't even understand how this can be) (everything in the same browser):
 1.  5.6.2 -> 5.7
 2.  5.7->5.6.2
 3.  Clear cache, cookies, etc.
 4.  5.6.2 -> 5.7  ==> Works!


 == The updating scenario explored on Opera
 - 5.6.2 => 5.7 ==> Doesn't work

 == The updating scenario explored on Firefox & Brave
 - 5.6.2 => 5.7 ==> Works!

 Also
 - A diff checker between first load and 2nd load did not show anything (I
 thought about ?ver=x)
 - Nothing comes up in the console
 - The issues have been replicated locally & on 2 different servers


 Maybe someone can see what's the problem trough the results above. At
 first I thought it might be cache related, then, it seems it's how
 browsers handle things. This is tricky because it needs to be caught at
 its first load in the browser. Would be nice to have a fix in 5.7.1
 because that comparison block looks pretty nice!

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Ticket URL: <https://core.trac.wordpress.org/ticket/52758>
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