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Script Loader: Move delayed head script to footer when there is a blocking footer dependent.

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This prevents a performance regression when a blocking script is enqueued in the footer which depends on a delayed script in the `head` (with `async` or `defer`). In order to preserve the execution order, a delayed dependency must fall back to blocking when there is a blocking dependent. But since it was originally delayed (and thus executes similarly to a footer script), it does not need to be in the head and can be moved to the footer. This prevents blocking the critical rendering path.

Props adamsilverstein, westonruter, flixos90.
Fixes #59599.
See #12009.

Built from https://develop.svn.wordpress.org/trunk@56933


git-svn-id: http://core.svn.wordpress.org/trunk@56444 1a063a9b-81f0-0310-95a4-ce76da25c4cd
This commit is contained in:
Weston Ruter 2023-10-13 18:46:21 +00:00
parent a17a3ca214
commit 793eaf7f19
2 changed files with 39 additions and 1 deletions
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38
wp-includes/class-wp-scripts.php
View File

@ -231,6 +231,25 @@ class WP_Scripts extends WP_Dependencies {
return true;
}
/**
* Checks whether all dependents of a given handle are in the footer.
*
* If there are no dependents, this is considered the same as if all dependents were in the footer.
*
* @since 6.4.0
*
* @param string $handle Script handle.
* @return bool Whether all dependents are in the footer.
*/
private function are_all_dependents_in_footer( $handle ) {
foreach ( $this->get_dependents( $handle ) as $dep ) {
if ( isset( $this->groups[ $dep ] ) && 0 === $this->groups[ $dep ] ) {
return false;
}
}
return true;
}
/**
* Processes a script dependency.
*
@ -281,6 +300,25 @@ class WP_Scripts extends WP_Dependencies {
$intended_strategy = '';
}
/*
* Move this script to the footer if:
* 1. The script is in the header group.
* 2. The current output is the header.
* 3. The intended strategy is delayed.
* 4. The actual strategy is not delayed.
* 5. All dependent scripts are in the footer.
*/
if (
0 === $group &&
0 === $this->groups[ $handle ] &&
$intended_strategy &&
! $this->is_delayed_strategy( $strategy ) &&
$this->are_all_dependents_in_footer( $handle )
) {
$this->in_footer[] = $handle;
return false;
}
if ( $conditional ) {
$cond_before = "<!--[if {$conditional}]>\n";
$cond_after = "<![endif]-->\n";

2
wp-includes/version.php
View File

@ -16,7 +16,7 @@
*
* @global string $wp_version
*/
$wp_version = '6.4-beta4-56932';
$wp_version = '6.4-beta4-56933';
/**
* Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.