[wp-trac] [WordPress Trac] #33001: Customizer loads wp-a11y.js multiple times

[WordPress Trac]

#33001: Customizer loads wp-a11y.js multiple times
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 Reporter:  afercia                    |      Owner:
     Type:  defect (bug)               |     Status:  new
 Priority:  normal                     |  Milestone:  4.3
Component:  Customize                  |    Version:  4.2
 Severity:  normal                     |   Keywords:  needs-patch
  Focuses:  accessibility, javascript  |
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 Depending on the screen, the Customizer loads the `wp-a11y.js` script
 multiple times, thus creating multiple live regions. Given the way screen
 readers deal with live regions, which is very prone to inconsistencies, we
 should avoid having multiple live regions.

 As far as I see, to load faster the Customizer uses the "customize loader"
 in 3 places:
 - in the Dashboard and for a good reason, see [changeset:22089]
 - in the themes.php screen
 - in the update.php screen when updating a theme

 in these screens, there will be 3 documents with 3 bodies so the live
 regions will be appended to each body: the main body, the "customize
 loader" iframe document body, and the Customizer preview iframe document
 body.

 In the other screens, just 2 times: in the main body and in the Customizer
 preview iframe body.

 Worth noting live regions are currently appended in the Dashboard, where
 they're unnecessary.

 (please consider in the first screenshot I've edited the DOM
 representation in the console removing lots of stuff to make it shorter
 and fit in the screenshot)

 [[Image(https://cldup.com/MDwcEZ10VS.png)]]

 [[Image(https://cldup.com/BYQxEDi8rj.png)]]

 To my understanding this is not caused by the Customizer itself and it's
 more related to the way `wp-a11y.js` is specified as dependency. Currently
 it's a dependency of 'customize-base' and 'customize-nav-menus'. For the
 other screens it's a dependency of 'theme' and 'updates'.
 About the Customizer, maybe setting it as dependency at a later stage
 (e.g. 'customize-controls') would fix this. Would like to hear the opinion
 of someone more familiar with script dependencies than me though.

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Ticket URL: <https://core.trac.wordpress.org/ticket/33001>
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