[wp-trac] [WordPress Trac] #12009: Add support for HTML 5 "async" and "defer" attributes

[WordPress Trac]

#12009: Add support for HTML 5 "async" and "defer" attributes
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 Reporter:  Otto42         |       Owner:  azaozz
     Type:  enhancement    |      Status:  reopened
 Priority:  normal         |   Milestone:  Future Release
Component:  Script Loader  |     Version:  4.6
 Severity:  normal         |  Resolution:
 Keywords:                 |     Focuses:
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Comment (by westonruter):

 Replying to [comment:46 azaozz]:
 > Currently there are few tickets that touch on some parts of
 updating/refactoring script-loader. IMHO best would be to combine them and
 really refactor it. Implement HTTP/2 + `defer`, output all in the head,
 retire load-scripts.php, etc. etc. Ideally this should be done before
 Gutenberg lands in core.

 Retiring `load-scripts.php` I think can also/rather be accomplished via
 service workers: #36995.

 > The `async` attribute cannot be used in script-loader because the script
 doesn't follow execution order. If you are adding a stand-alone script
 that has no dependencies and other scripts don't depend on it, there is no
 point adding it to script loader at all.

 It would make sense to me that if you register a script with an `async`
 flag ''and'' a non-empty `deps` that this should result in a
 `_doing_it_wrong()`.

 It makes sense to me to use the WP dependency system even if there are no
 dependencies because it provides a standard programatic interface for
 registering and outputting scripts. Core or a plugin could register an
 `async` script and then it or other plugins could just simply enqueue it
 and be done with it, as is standard in WP. A plugin could check to see if
 a script is already registered and prevent registering and enqueueing
 their own if it already exists. Also no worrying about adding an action to
 print a manually-crafted `script` tag. No (less) worrying about duplicated
 scripts being output.

 > Currently there are few tickets that touch on some parts of
 updating/refactoring script-loader. IMHO best would be to combine them and
 really refactor it. Implement HTTP/2 + `defer`, output all in the head,
 retire load-scripts.php, etc. etc. Ideally this should be done before
 Gutenberg lands in core.

 Just to be clear, I'm talking about WP script dependencies generally not
 `load-scripts.php` specifically. I think there is good value in adding
 `async` and `defer` support to the existing `WP_Scripts` system so that we
 can take advantage of them now. Since you noted that less than 25% of the
 Web is on HTTP/2, I don't think we should let it be the blocker for us to
 encourage best practices now for script loading for themes and plugins via
 `async` and `defer`. HTTP/2 definitely won't be available before
 Gutenberg.

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Ticket URL: <https://core.trac.wordpress.org/ticket/12009#comment:47>
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