Script Loader: Disable script and style concatenation by default by haqadn · Pull Request #13090 · WordPress/wordpress-develop

haqadn · 2026-08-16T22:57:12Z

✅ Committed in r64320 (cc891ab).

Trac ticket: https://core.trac.wordpress.org/ticket/57548

Flips the fallback in wp_should_concatenate_admin_scripts() so an undefined CONCATENATE_SCRIPTS resolves to false instead of true. load-scripts.php and load-styles.php become opt-in — sites that want the current behavior can define( 'CONCATENATE_SCRIPTS', true ).

Since r64120, wp_should_concatenate_admin_scripts() holds the default that script_concat_settings() gives the $concatenate_scripts global, and it is also what the login screen's prefetching uses to predict whether the admin will concatenate. Flipping the default there changes both at once, so they cannot disagree. (This PR originally flipped it inline in script_concat_settings(); the merge with trunk after r64120 moved the change into the new function, along with the function's docs and its filter's @param, which state the default, and updated the tests of the default.)

Scope is narrower than the constant's name suggests. script_concat_settings() only applies this default on admin screens and the login screen, and leaves the global false everywhere else, so only wp-admin and the login screen change. The concatenation code paths themselves are untouched.

Separately, TinyMCE is now always registered as separate files instead of the prebuilt wp-tinymce.js bundle, whether or not scripts are concatenated. See "Notes about TinyMCE" below.

Two reasons to make this the default:

Concatenation is the root of a class of bugs that only appear when it is on. SCRIPT_DEBUG being ignored (#52879), translations not printing for concatenated handles (#50999), and "use strict" leaking between bundled scripts (#65515) are all conditions a stock install currently ships into. Defaulting off takes wp-admin off that path.
It is what makes r64120 do anything. That change (Script Loader: Prefetch assets for the next admin screen #13084) prefetches the admin's individual assets from the login screen and the editor's stylesheets from the Dashboard and post lists, but only when concatenation is off. Under today's default it is inert on a stock install; with this flip it applies by default, which is the pairing the two changes were intended to have.

Performance

The cold-cache performance trade-off was the open question when this PR was opened. The benchmarks on #13084 answer it for the main path into the admin: logging in with an empty browser cache. They compare today's default (concatenation on) with this PR's configuration (concatenation off, with r64120's prefetching), and with concatenation off and nothing prefetched as a control. Medians, with prefetching relative to today's default:

	Fast 4G	Slow 4G
Dashboard LCP	−25%	−47% (1.86 s vs 3.49 s)
Dashboard DOMContentLoaded	+2%	0%
Posts list FCP	−58%	−70%
Block editor FCP	−44%	−70%
Block editor ready (post title visible)	−11%	−15%
Login screen FCP	+11%	−5%
Login screen `load`	+32%	+32%

Full method and raw numbers: login → Dashboard (10 runs per arm) and login → Dashboard → Posts list → block editor (3 runs per arm).

Turning concatenation off with prefetching is faster than today's default because a concatenated bundle is only reused when its exact list of handles matches. The Posts list and the editor each build bundles that differ from the Dashboard's, so they download the common admin CSS and jQuery again, while individual files carry over from screen to screen. The login screen's higher load time comes from concatenation being off there, not from the prefetching, and its FCP barely moves.

What the benchmarks do not cover:

Reaching the admin without passing through the login screen, e.g. with a "Remember me" cookie still valid after the browser cache was cleared. Nothing is prefetched in that case, and the cold Dashboard is slower than today: about 280–310 ms of LCP, and 0.5 s (Fast 4G) to 1.2–1.9 s (Slow 4G) of DOMContentLoaded. The Posts list is still faster without concatenation, and the editor is about even.
Repeat visits with a warm cache, where the configurations should converge. As @sgomes pointed out, the benefit of prefetching is mostly once per user, until the cache is evicted.
HTTP/2 and browsers other than Chrome. All runs were on one machine, over HTTP/1.1 on localhost with DevTools throttling. HTTP/2 should narrow the gaps in both directions, since request count matters less there.
A concatenated site prefetching its own bundles. Part of the lead comes from prefetching as such, not only from dropping concatenation.
Compression dictionaries, discussed on the ticket, which are not part of this comparison.

Notes about TinyMCE

TinyMCE is now always registered as separate files: TinyMCE core (wp-tinymce-root) and the compat3x plugin (wp-tinymce). When an editor is initialized, TinyMCE fetches its theme, plugins and skin itself. The prebuilt wp-tinymce.js bundle is no longer registered.

Until now, the bundle was registered only when scripts were both concatenated and compressed. Concatenation is now off by default. $compress_scripts hasn't compressed anything since r43580 and r44651, and it is slated for removal (Core-66053). So TinyMCE's registration no longer depends on either. The second parameter of wp_register_tinymce_scripts() is unused, so it is deprecated and renamed to $deprecated. A site that wants the bundle can still register it under the wp-tinymce handle:

add_action( 'wp_default_scripts', static function ( WP_Scripts $scripts ): void {
	$scripts->remove( array( 'wp-tinymce', 'wp-tinymce-root' ) );
	$scripts->add( 'wp-tinymce', includes_url( 'js/tinymce/wp-tinymce.js' ), array(), $GLOBALS['tinymce_version'] );
}, 11 );

The bundle holds TinyMCE core, the modern theme and all 22 plugins: 671 KB, versus 369 KB for core plus compat3x. Whether leaving it out helps depends on whether TinyMCE is initialized.

Loaded but not initialized: smaller and faster. The block editor loads TinyMCE on every screen. It initializes TinyMCE only when a Classic block's "Edit" button is clicked, even if the post already contains a Classic block. Block editor page load, before any click:

	Fast 4G	Slow 4G
TinyMCE transfer	219 → 125 KB	219 → 125 KB
DOMContentLoaded and `load`	−73 ms	−576 ms
FCP	unchanged	unchanged

Initialized: slower. This covers the classic editor, and a Classic block once "Edit" is clicked:

	Fast 4G	Slow 4G
Classic editor: TinyMCE ready	4.68 → 5.38 s (+15%)	17.60 → 19.87 s (+13%)
Classic editor: DOMContentLoaded	−104 ms	−567 ms
Classic editor: `load`	+537 ms	+1,845 ms
Classic editor: FCP	unchanged	unchanged
Classic block: from "Edit" click to ready	254 → 1,034 ms	896 → 3,682 ms

The bytes are about the same: 233 KB versus 228 KB of TinyMCE in the classic editor, over 20 more requests. The delay comes from the order the files load in. Once its core has run, TinyMCE requests the rest in three rounds, each waiting for the last:

the theme;
the 18 plugins the editor uses, in parallel;
the skin.

With the bundle, the "Edit" click needs 2 requests (27 KB). Without it, the click needs 21 requests (127 KB).

TinyMCE is being phased out, so this cost is accepted. It could be reduced by registering the theme and plugins as their own handles and enqueuing them where the classic editor initializes TinyMCE. They would then load from the page's HTML instead of waiting for TinyMCE to request them. That would not help the Classic block, which only fetches them when "Edit" is clicked.

Method: medians of 5 cold-cache runs per arm, run alternately, with a real login each run. Chrome over HTTP/1.1 on localhost with DevTools throttling, concatenation and SCRIPT_DEBUG off, all plugins disabled. HTTP/2 should shrink the cost of the extra requests.

Testing instructions

Use an install with neither CONCATENATE_SCRIPTS nor SCRIPT_DEBUG defined in wp-config.php.
Load any wp-admin screen (the Dashboard is fine) and view source. There should be no requests to load-scripts.php or load-styles.php — every handle appears as its own <script src> or <link href>.
Confirm the admin behaves normally: menus, the list tables, and the block editor should all load without console errors.
In the block editor, add a Classic block and click "Edit". The editor should open and work, and the browser's Network panel should show tinymce.min.js and plugins/compat3x/plugin.min.js, followed by the modern theme and the editor plugins as separate requests, with no wp-tinymce.js. Do the same in the classic editor (e.g. with the Classic Editor plugin active), confirming the Visual tab works.
Load wp-login.php and view source. There should be <link rel="prefetch"> tags for the admin's stylesheets and head scripts near the end of the page, since the login screen now predicts that the admin will not concatenate.
Add define( 'CONCATENATE_SCRIPTS', true ); to wp-config.php and reload the same screens. Both load-scripts.php and load-styles.php should reappear on the admin screen, confirming the opt-in path still works, and the login screen should print no prefetch links. TinyMCE should still load as separate files, not as wp-tinymce.js.

Use of AI Tools

AI assistance: Yes
Tool(s): Claude Code
Model(s): Claude Opus 5, Claude Opus 5.5
Used for: Making the change, running the test suite and confirming the pre-existing failures against baseline, and drafting this description. Reviewed by me.

The merge with trunk after r64120, moving the change into wp_should_concatenate_admin_scripts() and updating its tests and this description (including the performance summary from the #13084 benchmarks), was done by @westonruter with Claude Code (Claude Opus 5.5).

Always registering TinyMCE as separate files, deprecating the second parameter of wp_register_tinymce_scripts(), benchmarking TinyMCE with and without the bundle, and the matching updates to this description were also done by @westonruter with Claude Code (Claude Opus 5.5).

github-actions · 2026-08-16T23:00:17Z

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Test this pull request with WordPress Playground.

Flips the fallback in `script_concat_settings()` so an undefined `CONCATENATE_SCRIPTS` resolves to `false` instead of `true`, making `load-scripts.php` and `load-styles.php` opt-in. Sites that want the previous behaviour can define the constant as `true`. The concatenation code paths are unchanged, and the surrounding guard already forces the global to `false` outside of `is_admin()` and `login_init`, so only wp-admin and the login screen are affected. See #57548.

Trunk moved the default for the `$concatenate_scripts` global out of `script_concat_settings()` and into `wp_should_concatenate_admin_scripts()`, which the login screen's prefetching also uses to predict whether the admin will concatenate. The conflict in `script_concat_settings()` is resolved to trunk's version, and this branch's change, making an undefined `CONCATENATE_SCRIPTS` mean `false` rather than `true`, is applied in `wp_should_concatenate_admin_scripts()` instead, along with the function's description and its filter's `@param`, which state the default. The prefetching therefore follows the new default too. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

…fault Two tests still expected an undefined `CONCATENATE_SCRIPTS` to mean concatenation unless `SCRIPT_DEBUG` is on. They passed when run from `src/`, where `SCRIPT_DEBUG` is on and turns concatenation off whatever the default, but would fail where it is off. They now expect no concatenation unless the constant is defined as true. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

TinyMCE was registered as the prebuilt `wp-tinymce.js` bundle only when scripts were both concatenated and compressed, and otherwise as TinyMCE core plus the compat3x plugin. Both conditions are on their way out: concatenation is now off by default, and `$compress_scripts` has not compressed anything since PHP compression was removed from the loaders in r43580 and from `wp-tinymce.php` in r44651. TinyMCE is now registered as the separate files regardless, which is how it is served on the front end and in the admin by default. The bundle holds the modern theme and all 22 plugins, which TinyMCE otherwise loads itself only when an editor is initialized. The block editor loads TinyMCE on every screen but only initializes it for a Classic block, so most screens skip about 300 KB. The `$force_uncompressed` parameter is now unused. The script_concat_settings() call stays, since this is where an admin screen settles the concatenation settings, as the `wp_should_concatenate_admin_scripts` filter documents. A site can still register the bundle under the `wp-tinymce` handle itself. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

The `$wp_scripts` global is typed as `mixed`, which PHPStan rejects as the `WP_Scripts` argument to wp_register_tinymce_scripts(). The wp_scripts() accessor returns a `WP_Scripts` instance, initializing the global first if needed. The `true` passed as the second argument is dropped too, since that parameter is no longer used. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Since TinyMCE is always registered as separate files, the `$force_uncompressed` parameter has nothing left to force. It is renamed to `$deprecated` and typed with `@phpstan-param false`, as for other deprecated parameters, so that PHPStan reports any caller still passing `true`. Passing a truthy value also triggers _deprecated_argument(), which uses the parameter and so resolves its `function.unusedParameter` error. _WP_Editors::force_uncompressed_tinymce() no longer passes `true`, so it does not trigger the notice. The signature also gains a `void` return type, which resolves the `missingType.return` error reported on the changed line. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

The deprecation notice in wp_register_tinymce_scripts() was triggered only for a non-empty `$deprecated`, so a caller passing `null`, `0` or an empty string went unnoticed. Since `false` is the only value the parameter accepts, as its `@phpstan-param` says, any other value now triggers the notice. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

github-actions · 2026-10-12T22:39:36Z

The following accounts have interacted with this PR and/or linked issues. I will continue to update these lists as activity occurs. You can also manually ask me to refresh this list by adding the props-bot label.

Core Committers: Use this line as a base for the props when committing in SVN:

Props adnan007, westonruter.

To understand the WordPress project's expectations around crediting contributors, please review the Contributor Attribution page in the Core Handbook.

westonruter · 2026-10-13T03:55:38Z

With SCRIPT_DEBUG set to false, this is the difference between trunk and this PR, showing that CONCATENATE_SCRIPTS is no longer defaulting to on:

Dashboard

--- trunk.html	2026-10-12 20:49:55
+++ pr.html	2026-10-12 20:50:08
@@ -24,8 +24,9 @@
 <script>
 Object.assign( window, {"ajaxurl":"/wp-admin/admin-ajax.php","pagenow":"dashboard","typenow":"","adminpage":"index-php","thousandsSeparator":",","decimalPoint":".","isRtl":0} );
 </script>
-<link rel='stylesheet' href='http://localhost:8000/wp-admin/load-styles.php?c=1&amp;dir=ltr&amp;load%5Bchunk_0%5D=dashicons,admin-bar,site-health,common,forms,admin-menu,dashboard,list-tables,edit,revisions,media,themes,about,nav-menus,wp-poi&amp;load%5Bchunk_1%5D=nter,widgets,site-icon,l10n,wp-tooltip,buttons,wp-auth-check&amp;ver=7.2-alpha-63166-src' media='all' />
-<style>
+<link rel='stylesheet' id='dashicons-css' href='http://localhost:8000/wp-includes/css/dashicons.min.css?ver=7.2-alpha-63166-src' media='all' />
+<link rel='stylesheet' id='admin-bar-css' href='http://localhost:8000/wp-includes/css/admin-bar.min.css?ver=7.2-alpha-63166-src' media='all' />
+<style id="admin-bar-inline-css">
 		#wpadminbar .quicklinks li img.blavatar {
 			border-radius: 2px;
 		}
@@ -54,11 +55,30 @@
 			}
 		}
 @media print { #wpadminbar { display:none; } }
-/*# sourceURL=css-inline-concat-dashicons%2Cadmin-bar%2Csite-health%2Ccommon%2Cforms%2Cadmin-menu%2Cdashboard%2Clist-tables%2Cedit%2Crevisions%2Cmedia%2Cthemes%2Cabout%2Cnav-menus%2Cwp-pointer%2Cwidgets%2Csite-icon%2Cl10n%2Cwp-tooltip%2Cbuttons%2Cwp-auth-check */
+/*# sourceURL=admin-bar-inline-css */
 </style>
+<link rel='stylesheet' id='site-health-css' href='http://localhost:8000/wp-admin/css/site-health.min.css?ver=7.2-alpha-63166-src' media='all' />
 <link rel='stylesheet' id='thickbox-css' href='http://localhost:8000/wp-includes/js/thickbox/thickbox.css?ver=7.2-alpha-63166-src' media='all' />
+<link rel='stylesheet' id='common-css' href='http://localhost:8000/wp-admin/css/common.min.css?ver=7.2-alpha-63166-src' media='all' />
+<link rel='stylesheet' id='forms-css' href='http://localhost:8000/wp-admin/css/forms.min.css?ver=7.2-alpha-63166-src' media='all' />
+<link rel='stylesheet' id='admin-menu-css' href='http://localhost:8000/wp-admin/css/admin-menu.min.css?ver=7.2-alpha-63166-src' media='all' />
+<link rel='stylesheet' id='dashboard-css' href='http://localhost:8000/wp-admin/css/dashboard.min.css?ver=7.2-alpha-63166-src' media='all' />
+<link rel='stylesheet' id='list-tables-css' href='http://localhost:8000/wp-admin/css/list-tables.min.css?ver=7.2-alpha-63166-src' media='all' />
+<link rel='stylesheet' id='edit-css' href='http://localhost:8000/wp-admin/css/edit.min.css?ver=7.2-alpha-63166-src' media='all' />
+<link rel='stylesheet' id='revisions-css' href='http://localhost:8000/wp-admin/css/revisions.min.css?ver=7.2-alpha-63166-src' media='all' />
+<link rel='stylesheet' id='media-css' href='http://localhost:8000/wp-admin/css/media.min.css?ver=7.2-alpha-63166-src' media='all' />
+<link rel='stylesheet' id='themes-css' href='http://localhost:8000/wp-admin/css/themes.min.css?ver=7.2-alpha-63166-src' media='all' />
+<link rel='stylesheet' id='about-css' href='http://localhost:8000/wp-admin/css/about.min.css?ver=7.2-alpha-63166-src' media='all' />
+<link rel='stylesheet' id='nav-menus-css' href='http://localhost:8000/wp-admin/css/nav-menus.min.css?ver=7.2-alpha-63166-src' media='all' />
+<link rel='stylesheet' id='wp-pointer-css' href='http://localhost:8000/wp-includes/css/wp-pointer.min.css?ver=7.2-alpha-63166-src' media='all' />
+<link rel='stylesheet' id='widgets-css' href='http://localhost:8000/wp-admin/css/widgets.min.css?ver=7.2-alpha-63166-src' media='all' />
+<link rel='stylesheet' id='site-icon-css' href='http://localhost:8000/wp-admin/css/site-icon.min.css?ver=7.2-alpha-63166-src' media='all' />
+<link rel='stylesheet' id='l10n-css' href='http://localhost:8000/wp-admin/css/l10n.min.css?ver=7.2-alpha-63166-src' media='all' />
 <link rel='stylesheet' id='wp-base-styles-css' href='http://localhost:8000/wp-content/plugins/gutenberg/build/styles/base-styles/admin-schemes.min.css?ver=trunk' media='all' />
+<link rel='stylesheet' id='wp-tooltip-css' href='http://localhost:8000/wp-admin/css/wp-tooltip.min.css?ver=7.2-alpha-63166-src' media='all' />
+<link rel='stylesheet' id='buttons-css' href='http://localhost:8000/wp-includes/css/buttons.min.css?ver=7.2-alpha-63166-src' media='all' />
 <link rel='stylesheet' id='colors-css' href='http://localhost:8000/wp-admin/css/colors/modern/colors.min.css?ver=7.2-alpha-63166-src' media='all' />
+<link rel='stylesheet' id='wp-auth-check-css' href='http://localhost:8000/wp-includes/css/wp-auth-check.min.css?ver=7.2-alpha-63166-src' media='all' />
 <link rel='stylesheet' id='wp-theme-css' href='http://localhost:8000/wp-content/plugins/gutenberg/build/styles/theme/design-tokens.min.css?ver=trunk' media='all' />
 <link rel='stylesheet' id='wp-components-css' href='http://localhost:8000/wp-content/plugins/gutenberg/build/styles/components/style.min.css?ver=24.1.0' media='all' />
 <link rel='stylesheet' id='wp-preferences-css' href='http://localhost:8000/wp-content/plugins/gutenberg/build/styles/preferences/style.min.css?ver=24.1.0' media='all' />
@@ -66,9 +86,11 @@
 <style id="wp-view-transitions-admin-inline-css">
 /*! This file is auto-generated */
 @media (prefers-reduced-motion:no-preference){@view-transition{navigation:auto}#adminmenu>.menu-top{view-transition-name:attr(id type(<custom-ident>),none)}}
+/*# sourceURL=wp-view-transitions-admin-inline-css */
 </style>
 <style id="dominant-color-admin-styles-inline-css">
 .wp-core-ui .attachment-preview[data-dominant-color]:not(.has-transparency) { background-color: var(--dominant-color); }
+/*# sourceURL=dominant-color-admin-styles-inline-css */
 </style>
 <link rel='stylesheet' id='wp-notices-css' href='http://localhost:8000/wp-content/plugins/gutenberg/build/styles/notices/style.min.css?ver=24.1.0' media='all' />
 <link rel='stylesheet' id='wp-block-editor-css' href='http://localhost:8000/wp-content/plugins/gutenberg/build/styles/block-editor/style.min.css?ver=24.1.0' media='all' />
@@ -89,6 +111,7 @@
 		background: none !important;
 		padding: 0 !important;
 	}
+/*# sourceURL=wp-emoji-styles-inline-css */
 </style>
 <style class="wp-fonts-local">
 @font-face{font-family:Manrope;font-style:normal;font-weight:200 800;font-display:fallback;src:url('http://localhost:8000/wp-content/themes/twentytwentyfive/assets/fonts/manrope/Manrope-VariableFont_wght.woff2') format('woff2');}
@@ -289,11 +312,14 @@
 @font-face{font-family:"Fira Sans";font-style:normal;font-weight:900;font-display:fallback;src:url('http://localhost:8000/wp-content/themes/twentytwentyfive/assets/fonts/fira-sans/FiraSans-Black.woff2') format('woff2');}
 @font-face{font-family:"Fira Sans";font-style:italic;font-weight:900;font-display:fallback;src:url('http://localhost:8000/wp-content/themes/twentytwentyfive/assets/fonts/fira-sans/FiraSans-BlackItalic.woff2') format('woff2');}
 </style>
-<script>
-var userSettings = {"url":"/","uid":"1","time":"1791863384","secure":""};
-//# sourceURL=js-inline-concat-jquery-core%2Cjquery-migrate%2Cutils%2Cwp-polyfill
+<script id="jquery-core-js" src="http://localhost:8000/wp-includes/js/jquery/jquery.min.js?ver=3.7.1"></script>
+<script id="jquery-migrate-js" src="http://localhost:8000/wp-includes/js/jquery/jquery-migrate.min.js?ver=3.6.0"></script>
+<script id="utils-js-extra">
+var userSettings = {"url":"/","uid":"1","time":"1791863402","secure":""};
+//# sourceURL=utils-js-extra
 </script>
-<script src="http://localhost:8000/wp-admin/load-scripts.php?c=1&#038;load%5Bchunk_0%5D=jquery-core,jquery-migrate,utils,wp-polyfill&#038;ver=7.2-alpha-63166-src"></script>
+<script id="utils-js" src="http://localhost:8000/wp-includes/js/utils.min.js?ver=7.2-alpha-63166-src"></script>
+<script id="wp-polyfill-js" src="http://localhost:8000/wp-includes/js/dist/vendor/wp-polyfill.min.js?ver=3.15.0"></script>
 <script id="react-js" src="http://localhost:8000/wp-content/plugins/gutenberg/build/scripts/vendors/react-19.min.js?ver=19.3.0"></script>
 <script id="react-dom-js" src="http://localhost:8000/wp-content/plugins/gutenberg/build/scripts/vendors/react-dom-19.min.js?ver=19.3.0"></script>
 <script id="react-jsx-runtime-js" src="http://localhost:8000/wp-content/plugins/gutenberg/build/scripts/vendors/react-jsx-runtime-19.min.js?ver=19.3.0"></script>
@@ -304,7 +330,55 @@
 			window.history.replaceState( null, null, document.getElementById( 'wp-admin-canonical' ).href + window.location.hash );
 		}
 	</script>
-	<meta name="viewport" content="width=device-width,initial-scale=1.0"></head>
+	<meta name="viewport" content="width=device-width,initial-scale=1.0"><link rel='prefetch' href='http://localhost:8000/wp-content/plugins/gutenberg/build/styles/edit-post/style.min.css?ver=24.1.0' as='style' />
+<link rel='prefetch' href='http://localhost:8000/wp-content/plugins/gutenberg/build/styles/block-directory/style.min.css?ver=24.1.0' as='style' />
+<link rel='prefetch' href='http://localhost:8000/wp-content/plugins/gutenberg/build/styles/format-library/style.min.css?ver=24.1.0' as='style' />
+<link rel='prefetch' href='http://localhost:8000/wp-includes/css/editor.min.css?ver=7.2-alpha-63166-src' as='style' />
+<link rel='prefetch' href='http://localhost:8000/wp-includes/css/media-views.min.css?ver=7.2-alpha-63166-src' as='style' />
+<link rel='prefetch' href='http://localhost:8000/wp-includes/js/imgareaselect/imgareaselect.css?ver=0.9.8' as='style' />
+<link rel='prefetch' href='http://localhost:8000/wp-content/plugins/gutenberg/build/styles/block-library/style.min.css?ver=trunk' as='style' />
+<link rel='prefetch' href='http://localhost:8000/wp-content/plugins/gutenberg/build/styles/widgets/style.min.css?ver=24.1.0' as='style' />
+<link rel='prefetch' href='http://localhost:8000/wp-content/plugins/gutenberg/build/styles/block-library/editor.min.css?ver=trunk' as='style' />
+<link rel='prefetch' href='http://localhost:8000/wp-includes/js/mediaelement/wp-mediaelement.min.css?ver=7.2-alpha-63166-src' as='style' />
+<link rel='prefetch' href='http://localhost:8000/wp-content/plugins/gutenberg/build/styles/block-library/reset.min.css?ver=trunk' as='style' />
+<link rel='prefetch' href='http://localhost:8000/wp-content/plugins/gutenberg/build/styles/block-editor/content.min.css?ver=trunk' as='style' />
+<link rel='prefetch' href='http://localhost:8000/wp-includes/js/mediaelement/mediaelementplayer-legacy.min.css?ver=4.2.17' as='style' />
+<script>
+( /**
+ * Prefetches the page's rel=prefetch links with fetch() in browsers that do not support rel=prefetch.
+ *
+ * @see https://caniuse.com/link-rel-prefetch
+ */
+() => {
+	if ( document.createElement( 'link' ).relList?.supports?.( 'prefetch' ) ) {
+		return;
+	}
+
+	const prefetch = () => {
+		for ( const link of /** @type {NodeListOf<HTMLLinkElement>} */ ( document.querySelectorAll( 'link[rel~="prefetch"][href]' ) ) ) {
+			fetch( link.href, { mode: 'no-cors', credentials: 'include', priority: 'low' } )
+				.then( ( response ) => response.blob() )
+				.catch( () => {} );
+		}
+	};
+
+	const schedule = () => {
+		if ( 'requestIdleCallback' in window ) {
+			window.requestIdleCallback( prefetch );
+		} else {
+			setTimeout( prefetch, 0 );
+		}
+	};
+
+	if ( 'complete' === document.readyState ) {
+		schedule();
+	} else {
+		window.addEventListener( 'load', schedule, { once: true } );
+	}
+} )();
+//# sourceURL=wp_prefetch_admin_assets
+</script>
+</head>
 <body class="wp-admin wp-core-ui no-js index-php auto-fold admin-bar branch-7-2 version-7-2 admin-color-modern locale-en-us no-customize-support svg wp-theme-twentytwentyfive">
 <script>
 document.body.className = document.body.className.replace( 'no-js', 'js' );
@@ -1059,7 +1133,7 @@
 <script id="wp-script-module-data-@nocache-bfcache/bfcache-invalidation" type="application/json">
 {"cookieName":"wordpress_bfcache_session_70490311fe7c84acda8886406a6d884b","initialSessionToken":"YqIe5DT40YwcqIdEUqe4hT50twOABommTsp3nqStC7f","debug":true,"i18n":{"logPrefix":"[Instant Back/Forward]","pageRestored":"Page restored from bfcache.","pageInvalidating":"Cached page is stale. Reloading...","pageInvalidated":"Page invalidated from cache via pageshow event handler.","notRestoredReasons":"Reasons page navigation not restored from bfcache:","infiniteReloadPrevented":"Prevented infinite reload."}}
 </script>
-<script src="http://localhost:8000/wp-admin/load-scripts.php?c=1&#038;load%5Bchunk_0%5D=hoverIntent&#038;ver=7.2-alpha-63166-src"></script>
+<script id="hoverIntent-js" src="http://localhost:8000/wp-includes/js/hoverIntent.min.js?ver=1.10.2"></script>
 <script id="wp-dom-ready-js" src="http://localhost:8000/wp-content/plugins/gutenberg/build/scripts/dom-ready/index.min.js?ver=3fe927cab37bf38d6a23"></script>
 <script id="wp-hooks-js" src="http://localhost:8000/wp-content/plugins/gutenberg/build/scripts/hooks/index.min.js?ver=f0f188028580e8dc1255"></script>
 <script id="wp-i18n-js" src="http://localhost:8000/wp-content/plugins/gutenberg/build/scripts/i18n/index.min.js?ver=1dfe7db3940c23ea9216"></script>

Login Screen

--- trunk.html	2026-10-12 20:53:15
+++ pr.html	2026-10-12 20:52:57
@@ -7,8 +7,13 @@
 if("sessionStorage" in window){try{for(var key in sessionStorage){if(key.indexOf("wp-autosave-")!=-1){sessionStorage.removeItem(key)}}}catch(e){}};
 </script>
 <meta name='robots' content='max-image-preview:large, noindex, noarchive' />
-<link rel='stylesheet' href='http://localhost:8000/wp-admin/load-styles.php?c=1&amp;dir=ltr&amp;load%5Bchunk_0%5D=dashicons,buttons,forms,l10n,wp-tooltip,login&amp;ver=7.2-alpha-63166-src' media='all' />
+<link rel='stylesheet' id='dashicons-css' href='http://localhost:8000/wp-includes/css/dashicons.min.css?ver=7.2-alpha-63166-src' media='all' />
+<link rel='stylesheet' id='buttons-css' href='http://localhost:8000/wp-includes/css/buttons.min.css?ver=7.2-alpha-63166-src' media='all' />
+<link rel='stylesheet' id='forms-css' href='http://localhost:8000/wp-admin/css/forms.min.css?ver=7.2-alpha-63166-src' media='all' />
+<link rel='stylesheet' id='l10n-css' href='http://localhost:8000/wp-admin/css/l10n.min.css?ver=7.2-alpha-63166-src' media='all' />
 <link rel='stylesheet' id='wp-base-styles-css' href='http://localhost:8000/wp-content/plugins/gutenberg/build/styles/base-styles/admin-schemes.min.css?ver=trunk' media='all' />
+<link rel='stylesheet' id='wp-tooltip-css' href='http://localhost:8000/wp-admin/css/wp-tooltip.min.css?ver=7.2-alpha-63166-src' media='all' />
+<link rel='stylesheet' id='login-css' href='http://localhost:8000/wp-admin/css/login.min.css?ver=7.2-alpha-63166-src' media='all' />
 <link rel='stylesheet' id='nocache-bfcache-opt-in-css' href='http://localhost:8000/wp-content/plugins/nocache-bfcache/css/bfcache-opt-in.css?ver=1.3.3' media='all' />
 	<meta name='referrer' content='strict-origin-when-cross-origin' />
 		<meta name="viewport" content="width=device-width, initial-scale=1.0" />
@@ -99,11 +104,14 @@
 <script id="wp-script-module-data-@nocache-bfcache/detect-scripting-enabled-at-login" type="application/json">
 {"cookieName":"nocache_bfcache_js_enabled","cookiePath":"/","siteCookiePath":"/","loginPostUrl":"http://localhost:8000/wp-login.php"}
 </script>
-<script>
+<script id="clipboard-js" src="http://localhost:8000/wp-includes/js/clipboard.min.js?ver=2.0.11"></script>
+<script id="jquery-core-js" src="http://localhost:8000/wp-includes/js/jquery/jquery.min.js?ver=3.7.1"></script>
+<script id="jquery-migrate-js" src="http://localhost:8000/wp-includes/js/jquery/jquery-migrate.min.js?ver=3.6.0"></script>
+<script id="zxcvbn-async-js-extra">
 var _zxcvbnSettings = {"src":"http://localhost:8000/wp-includes/js/zxcvbn.min.js"};
-//# sourceURL=js-inline-concat-clipboard%2Cjquery-core%2Cjquery-migrate%2Czxcvbn-async
+//# sourceURL=zxcvbn-async-js-extra
 </script>
-<script src="http://localhost:8000/wp-admin/load-scripts.php?c=1&#038;load%5Bchunk_0%5D=clipboard,jquery-core,jquery-migrate,zxcvbn-async&#038;ver=7.2-alpha-63166-src"></script>
+<script id="zxcvbn-async-js" src="http://localhost:8000/wp-includes/js/zxcvbn-async.min.js?ver=1.0"></script>
 <script id="wp-hooks-js" src="http://localhost:8000/wp-content/plugins/gutenberg/build/scripts/hooks/index.min.js?ver=f0f188028580e8dc1255"></script>
 <script id="wp-i18n-js" src="http://localhost:8000/wp-content/plugins/gutenberg/build/scripts/i18n/index.min.js?ver=1dfe7db3940c23ea9216"></script>
 <script id="wp-i18n-js-after">
@@ -129,6 +137,61 @@
 </script>
 <script id="user-profile-js" src="http://localhost:8000/wp-admin/js/user-profile.min.js?ver=7.2-alpha-63166-src"></script>
 <script id="wp-tooltip-js" src="http://localhost:8000/wp-includes/js/wp-tooltip.js?ver=7.2-alpha-63166-src"></script>
+<link rel='prefetch' href='http://localhost:8000/wp-includes/js/utils.min.js?ver=7.2-alpha-63166-src' as='script' />
+<link rel='prefetch' href='http://localhost:8000/wp-includes/css/admin-bar.min.css?ver=7.2-alpha-63166-src' as='style' />
+<link rel='prefetch' href='http://localhost:8000/wp-includes/css/wp-auth-check.min.css?ver=7.2-alpha-63166-src' as='style' />
+<link rel='prefetch' href='http://localhost:8000/wp-content/plugins/gutenberg/build/styles/commands/style.min.css?ver=24.1.0' as='style' />
+<link rel='prefetch' href='http://localhost:8000/wp-admin/css/common.min.css?ver=7.2-alpha-63166-src' as='style' />
+<link rel='prefetch' href='http://localhost:8000/wp-admin/css/admin-menu.min.css?ver=7.2-alpha-63166-src' as='style' />
+<link rel='prefetch' href='http://localhost:8000/wp-admin/css/dashboard.min.css?ver=7.2-alpha-63166-src' as='style' />
+<link rel='prefetch' href='http://localhost:8000/wp-admin/css/list-tables.min.css?ver=7.2-alpha-63166-src' as='style' />
+<link rel='prefetch' href='http://localhost:8000/wp-admin/css/edit.min.css?ver=7.2-alpha-63166-src' as='style' />
+<link rel='prefetch' href='http://localhost:8000/wp-admin/css/revisions.min.css?ver=7.2-alpha-63166-src' as='style' />
+<link rel='prefetch' href='http://localhost:8000/wp-admin/css/media.min.css?ver=7.2-alpha-63166-src' as='style' />
+<link rel='prefetch' href='http://localhost:8000/wp-admin/css/themes.min.css?ver=7.2-alpha-63166-src' as='style' />
+<link rel='prefetch' href='http://localhost:8000/wp-admin/css/about.min.css?ver=7.2-alpha-63166-src' as='style' />
+<link rel='prefetch' href='http://localhost:8000/wp-admin/css/nav-menus.min.css?ver=7.2-alpha-63166-src' as='style' />
+<link rel='prefetch' href='http://localhost:8000/wp-admin/css/widgets.min.css?ver=7.2-alpha-63166-src' as='style' />
+<link rel='prefetch' href='http://localhost:8000/wp-admin/css/site-icon.min.css?ver=7.2-alpha-63166-src' as='style' />
+<link rel='prefetch' href='http://localhost:8000/wp-content/plugins/gutenberg/build/styles/components/style.min.css?ver=24.1.0' as='style' />
+<link rel='prefetch' href='http://localhost:8000/wp-content/plugins/gutenberg/build/styles/preferences/style.min.css?ver=24.1.0' as='style' />
+<link rel='prefetch' href='http://localhost:8000/wp-includes/css/wp-pointer.min.css?ver=7.2-alpha-63166-src' as='style' />
+<link rel='prefetch' href='http://localhost:8000/wp-content/plugins/gutenberg/build/styles/theme/design-tokens.min.css?ver=trunk' as='style' />
+<script>
+( /**
+ * Prefetches the page's rel=prefetch links with fetch() in browsers that do not support rel=prefetch.
+ *
+ * @see https://caniuse.com/link-rel-prefetch
+ */
+() => {
+	if ( document.createElement( 'link' ).relList?.supports?.( 'prefetch' ) ) {
+		return;
+	}
+
+	const prefetch = () => {
+		for ( const link of /** @type {NodeListOf<HTMLLinkElement>} */ ( document.querySelectorAll( 'link[rel~="prefetch"][href]' ) ) ) {
+			fetch( link.href, { mode: 'no-cors', credentials: 'include', priority: 'low' } )
+				.then( ( response ) => response.blob() )
+				.catch( () => {} );
+		}
+	};
+
+	const schedule = () => {
+		if ( 'requestIdleCallback' in window ) {
+			window.requestIdleCallback( prefetch );
+		} else {
+			setTimeout( prefetch, 0 );
+		}
+	};
+
+	if ( 'complete' === document.readyState ) {
+		schedule();
+	} else {
+		window.addEventListener( 'load', schedule, { once: true } );
+	}
+} )();
+//# sourceURL=wp_prefetch_admin_assets
+</script>
 	</body>
 	</html>

Scripts and styles in the admin and on the login screen are no longer concatenated by default. When the `CONCATENATE_SCRIPTS` constant is not defined, `wp_should_concatenate_admin_scripts()` now returns `false`, so `load-scripts.php` and `load-styles.php` are only used when a site opts in with `define( 'CONCATENATE_SCRIPTS', true )`. This is the next step toward retiring concatenation. It also puts into effect the prefetching of the admin's assets added in r64120, which only applies when concatenation is off. With an empty browser cache, logging in and then opening the Dashboard, the Posts list and the block editor was measured to be faster this way than with concatenation on. TinyMCE is now always registered as two separate files instead of the prebuilt `wp-tinymce.js` bundle: TinyMCE core and the compat3x plugin. The bundle was registered only when scripts were both concatenated and compressed, and since r43580 and r44651 the `$compress_scripts` global has not compressed anything, so the registration no longer depends on either. The block editor loads TinyMCE on every screen but initializes it only when a Classic block is edited, so it now downloads 369 KB for the two files instead of 671 KB for the bundle, which also holds the theme and all 22 plugins. When TinyMCE is initialized, in the classic editor or for a Classic block, it now requests them itself and takes longer to become ready, a cost deemed acceptable since the role TinyMCE is increasingly diminished. A site can still register the bundle under the `wp-tinymce` handle. The unused second parameter of `wp_register_tinymce_scripts()` is deprecated. Developed in #13090. Follow-up to r43580, r44114, r44651, r64120. Props adnan007, westonruter. See #57548, #66053. git-svn-id: https://develop.svn.wordpress.org/trunk@64320 602fd350-edb4-49c9-b593-d223f7449a82

Scripts and styles in the admin and on the login screen are no longer concatenated by default. When the `CONCATENATE_SCRIPTS` constant is not defined, `wp_should_concatenate_admin_scripts()` now returns `false`, so `load-scripts.php` and `load-styles.php` are only used when a site opts in with `define( 'CONCATENATE_SCRIPTS', true )`. This is the next step toward retiring concatenation. It also puts into effect the prefetching of the admin's assets added in r64120, which only applies when concatenation is off. With an empty browser cache, logging in and then opening the Dashboard, the Posts list and the block editor was measured to be faster this way than with concatenation on. TinyMCE is now always registered as two separate files instead of the prebuilt `wp-tinymce.js` bundle: TinyMCE core and the compat3x plugin. The bundle was registered only when scripts were both concatenated and compressed, and since r43580 and r44651 the `$compress_scripts` global has not compressed anything, so the registration no longer depends on either. The block editor loads TinyMCE on every screen but initializes it only when a Classic block is edited, so it now downloads 369 KB for the two files instead of 671 KB for the bundle, which also holds the theme and all 22 plugins. When TinyMCE is initialized, in the classic editor or for a Classic block, it now requests them itself and takes longer to become ready, a cost deemed acceptable since the role TinyMCE is increasingly diminished. A site can still register the bundle under the `wp-tinymce` handle. The unused second parameter of `wp_register_tinymce_scripts()` is deprecated. Developed in WordPress/wordpress-develop#13090. Follow-up to r43580, r44114, r44651, r64120. Props adnan007, westonruter. See #57548, #66053. Built from https://develop.svn.wordpress.org/trunk@64320 git-svn-id: http://core.svn.wordpress.org/trunk@63470 1a063a9b-81f0-0310-95a4-ce76da25c4cd

haqadn force-pushed the 57548-disable-concatenation-by-default branch from b5d66ea to 1e34129 Compare August 16, 2026 23:02

westonruter mentioned this pull request Sep 27, 2026

Script Loader: Prefetch assets for the next admin screen #13084

Closed

westonruter and others added 8 commits October 6, 2026 00:39

Merge branch 'trunk' into 57548-disable-concatenation-by-default

8329101

Merge branch 'trunk' into 57548-disable-concatenation-by-default

bc79401

westonruter marked this pull request as ready for review October 12, 2026 22:39

westonruter approved these changes Oct 13, 2026

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westonruter closed this Oct 13, 2026

gigitux mentioned this pull request Oct 21, 2026

Fix product script-count E2E test for WordPress 7.2 woocommerce/woocommerce#70085

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woocommercebot mentioned this pull request Oct 21, 2026

[Backport to release/11.3] Fix product script-count E2E test for WordPress 7.2 woocommerce/woocommerce#70091

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Script Loader: Disable script and style concatenation by default - #13090

Script Loader: Disable script and style concatenation by default#13090
haqadn wants to merge 9 commits into
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haqadn:57548-disable-concatenation-by-default

haqadn commented Aug 16, 2026 •

edited by westonruter

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Performance

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Test using WordPress Playground

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haqadn commented Aug 16, 2026 •

edited by westonruter

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