[wp-trac] [WordPress Trac] #59115: Use defer loading strategy for block view scripts

[WordPress Trac]

#59115: Use defer loading strategy for block view scripts
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 Reporter:  westonruter              |      Owner:  (none)
     Type:  defect (bug)             |     Status:  new
 Priority:  normal                   |  Milestone:  6.4
Component:  Editor                   |    Version:  trunk
 Severity:  normal                   |   Keywords:
  Focuses:  javascript, performance  |
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 In [https://github.com/WordPress/gutenberg/pull/52536 gutenberg#52536],
 the `defer` loading strategy was used for all block view scripts. This
 ticket is to backport the Gutenberg change to core. Script loading
 strategies were introduced in #12009.

 Currently block view scripts are registered without setting the
 `$in_footer` argument to `true`. For block themes, this means they will
 get printed in the `head` since `the_content` is processed before the
 `wp_head` action. For classic themes, however, `the_content` is processed
 ''after'' `wp_head`, resulting in the scripts being printed at
 `wp_footer`. Therefore, given that block view scripts have been printed in
 either the `head` or footer already, this means they can safely be made
 `defer`. Leaving them in the `head` is advantageous because it means the
 browser will discover these scripts earlier and start loading them with
 other page resources, but the presence of `defer` means that they will no
 longer block page rendering.

 This was similarly done for the wp-embed script in #58931.

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Ticket URL: <https://core.trac.wordpress.org/ticket/59115>
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