[wp-trac] [WordPress Trac] #63793: Parser-blocking scripts should render last in all cases to speed up page load

[WordPress Trac]

#63793: Parser-blocking scripts should render last in all cases to speed up page
load
---------------------------+-----------------------------
 Reporter:  kkmuffme       |      Owner:  (none)
     Type:  enhancement    |     Status:  new
 Priority:  normal         |  Milestone:  Awaiting Review
Component:  Script Loader  |    Version:
 Severity:  normal         |   Keywords:
  Focuses:                 |
---------------------------+-----------------------------
 Since <script> tags are render and parser blocking, WP should print all
 scripts that have neither defer/async (as effective strategy! the intended
 /data-wp-strategy is irrelevant) last*, after all other scripts.
 *taking into account dependencies of course. This means that all scripts
 that have dependencies or inline/localized, should also be moved as late
 as possible.

 {{{
 <script>var a = 'localized';</script>
 <script>console.log( 'aInlineScript' );</script>
 <script src="a.js" defer>
 <script src="b.js">
 <script src="c.js" async>
 <script src="d.js" defer>
 }}}

 Printing them in the following order, will significantly speed up reaching
 DOMContentLoaded, without having any impact on functionality:

 {{{
 <script src="d.js" defer>
 <script src="c.js" async>
 <script>var a = 'localized';</script>
 <script>console.log( 'aInlineScript' );</script>
 <script src="a.js" defer>
 <script src="b.js">
 }}}

 Additionally, afaik all "async" should be printed after all "defer", since
 executing the async JS will potentially delay further parsing (thus
 delaying the download of any unparsed scripts)

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Ticket URL: <https://core.trac.wordpress.org/ticket/63793>
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