Add fetchpriority=low support to script modules #70173

westonruter · 2025-05-21T01:41:29Z

This is to add support for the new $args parameter for wp_register_script_module()/wp_enqueue_script_module() for Core-61734 and proposed in WordPress/wordpress-develop#8815. When Gutenberg is active, the fetchpriority=low won't appear for script modules since the core script modules are overridden by Gutenberg.

github-actions · 2025-05-21T02:09:18Z

Flaky tests detected in 1ab3c34.
Some tests passed with failed attempts. The failures may not be related to this commit but are still reported for visibility. See the documentation for more information.

🔍 Workflow run URL: https://github.com/WordPress/gutenberg/actions/runs/17508853441
📝 Reported issues:

[Flaky Test] Redirection after template creation #60678 in /test/e2e/specs/site-editor/site-editor-url-navigation.spec.js
[Flaky Test] should refresh the page when stylesheet loading fails #71135 in /test/e2e/specs/interactivity/router-styles.spec.ts

…dd/script-module-fetchpriority-low

github-actions · 2025-09-03T21:10:11Z

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Co-authored-by: westonruter <[email protected]>
Co-authored-by: mukeshpanchal27 <[email protected]>
Co-authored-by: sirreal <[email protected]>

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lib/client-assets.php

* Allow scripts and script modules to be registered with a `fetchpriority` of `auto` (default), `high`, `low`: * When registering a script, add a `fetchpriority` arg to go alongside the `strategy` arg which was added for loading scripts with the `defer` and `async` loading strategies. See #12009. * For script modules, introduce an `$args` array parameter with a `fetchpriority` key to the `wp_register_script_module()`, and `wp_enqueue_script_module()` functions (and their respective underlying `WP_Script_Modules::register()` and `WP_Script_Modules::enqueue()` methods). This `$args` parameter corresponds with the same parameter used when registering non-module scripts. * Also for script modules, introduce `WP_Script_Modules::set_fetchpriority()` to override the `fetchpriority` for what was previously registered. * Emit a `_doing_it_wrong()` warning when an invalid `fetchpriority` value is used, and when `fetchpriority` is added to a script alias. * Include `fetchpriority` as an attribute on printed `SCRIPT` tags as well as on preload `LINK` tags for static script module dependencies. * Use a `fetchpriority` of `low` by default for: * Script modules used with the Interactivity API. For overriding this default in blocks, see [WordPress/gutenberg#71366 Gutenberg#71366]. * The `comment-reply` script. * Improve type checks and type hints. Developed in [#8815 GitHub PR], with [WordPress/gutenberg#70173 companion for Gutenberg]. Props westonruter, jonsurrell, swissspidy, luisherranz, kraftbj, audrasjb, dennysdionigi. Fixes #61734. git-svn-id: https://develop.svn.wordpress.org/trunk@60704 602fd350-edb4-49c9-b593-d223f7449a82

* Allow scripts and script modules to be registered with a `fetchpriority` of `auto` (default), `high`, `low`: * When registering a script, add a `fetchpriority` arg to go alongside the `strategy` arg which was added for loading scripts with the `defer` and `async` loading strategies. See #12009. * For script modules, introduce an `$args` array parameter with a `fetchpriority` key to the `wp_register_script_module()`, and `wp_enqueue_script_module()` functions (and their respective underlying `WP_Script_Modules::register()` and `WP_Script_Modules::enqueue()` methods). This `$args` parameter corresponds with the same parameter used when registering non-module scripts. * Also for script modules, introduce `WP_Script_Modules::set_fetchpriority()` to override the `fetchpriority` for what was previously registered. * Emit a `_doing_it_wrong()` warning when an invalid `fetchpriority` value is used, and when `fetchpriority` is added to a script alias. * Include `fetchpriority` as an attribute on printed `SCRIPT` tags as well as on preload `LINK` tags for static script module dependencies. * Use a `fetchpriority` of `low` by default for: * Script modules used with the Interactivity API. For overriding this default in blocks, see [WordPress/gutenberg#71366 Gutenberg#71366]. * The `comment-reply` script. * Improve type checks and type hints. Developed in [WordPress/wordpress-develop#8815 GitHub PR], with [WordPress/gutenberg#70173 companion for Gutenberg]. Props westonruter, jonsurrell, swissspidy, luisherranz, kraftbj, audrasjb, dennysdionigi. Fixes #61734. Built from https://develop.svn.wordpress.org/trunk@60704 git-svn-id: http://core.svn.wordpress.org/trunk@60040 1a063a9b-81f0-0310-95a4-ce76da25c4cd

* Allow scripts and script modules to be registered with a `fetchpriority` of `auto` (default), `high`, `low`: * When registering a script, add a `fetchpriority` arg to go alongside the `strategy` arg which was added for loading scripts with the `defer` and `async` loading strategies. See #12009. * For script modules, introduce an `$args` array parameter with a `fetchpriority` key to the `wp_register_script_module()`, and `wp_enqueue_script_module()` functions (and their respective underlying `WP_Script_Modules::register()` and `WP_Script_Modules::enqueue()` methods). This `$args` parameter corresponds with the same parameter used when registering non-module scripts. * Also for script modules, introduce `WP_Script_Modules::set_fetchpriority()` to override the `fetchpriority` for what was previously registered. * Emit a `_doing_it_wrong()` warning when an invalid `fetchpriority` value is used, and when `fetchpriority` is added to a script alias. * Include `fetchpriority` as an attribute on printed `SCRIPT` tags as well as on preload `LINK` tags for static script module dependencies. * Use a `fetchpriority` of `low` by default for: * Script modules used with the Interactivity API. For overriding this default in blocks, see [WordPress/gutenberg#71366 Gutenberg#71366]. * The `comment-reply` script. * Improve type checks and type hints. Developed in [WordPress/wordpress-develop#8815 GitHub PR], with [WordPress/gutenberg#70173 companion for Gutenberg]. Props westonruter, jonsurrell, swissspidy, luisherranz, kraftbj, audrasjb, dennysdionigi. Fixes #61734. Built from https://develop.svn.wordpress.org/trunk@60704 git-svn-id: https://core.svn.wordpress.org/trunk@60040 1a063a9b-81f0-0310-95a4-ce76da25c4cd

westonruter · 2025-09-03T22:20:34Z

See r60704 for the the changeset which added the default fetchpriority for Interactivity API scripts.

See #71366 which would allow for values other than low to be used by default for block view script modules.

lib/client-assets.php

mukeshpanchal27 · 2025-09-04T05:10:10Z

lib/client-assets.php

+
 		$path = gutenberg_url( "build-module/{$file_name}" );
-		wp_register_script_module( $script_module_id, $path, $script_module_data['dependencies'], $script_module_data['version'] );
+		wp_register_script_module( $script_module_id, $path, $script_module_data['dependencies'], $script_module_data['version'], $args ); // The $args parameter is new as of WP 6.9 per <https://core.trac.wordpress.org/ticket/61734>.


I checked to make sure extra arguments to functions don't cause errors/warnings/notices and that does seem to be the case 👍

Yeah, adding extra arguments is fine. No complaints going back even to PHP 4.3: https://3v4l.org/doYun

Any additional unnamed params could be obtained by the function via func_get_args().

Co-authored-by: Mukesh Panchal <[email protected]>

sirreal

Two things come to mind seeing this:

Script modules are registered with fetch priority. What if I enqueue a high fetch priority script that depends on a module registered with low? As the browser explores the dependency graph, will it determine that it should increase the priority of the dependency? Is that sort of priority dependence something that should be built into the core script modules system?

This makes all the Gutenberg script modules low. That's fine at the moment. Have you considered how this system may evolve as more modules are introduced? What mechanism might modules have to report what fetch priority they should have?

sirreal · 2025-09-04T09:24:10Z

lib/client-assets.php

+
 		$path = gutenberg_url( "build-module/{$file_name}" );
-		wp_register_script_module( $script_module_id, $path, $script_module_data['dependencies'], $script_module_data['version'] );
+		wp_register_script_module( $script_module_id, $path, $script_module_data['dependencies'], $script_module_data['version'], $args ); // The $args parameter is new as of WP 6.9 per <https://core.trac.wordpress.org/ticket/61734>.


I checked to make sure extra arguments to functions don't cause errors/warnings/notices and that does seem to be the case 👍

sirreal · 2025-09-04T09:31:02Z

lib/client-assets.php

 		}

+		/*
+		 * All script modules in Gutenberg are (currently) related to the Interactivity API which prioritizes server-side rendering.


There's @wordpress/a11y module that's not strictly an iAPI concept.

https://make.wordpress.org/core/2024/10/14/updates-to-script-modules-in-6-7/

I don't think other modules have been introduced, but I could have missed something. Should a11y be low as well?

Strictly, but it is only used by the interactivity-router, right? And it is used as a dynamic import, so it exists exclusively in the importmap and so there is no fetchpriority to print.

Granted, it could end up getting added as a static dependency. If I try doing that, I see that with this Gutenberg PR it is printed with fetchpriority=low, but if I try WP Core trunk then it omits fetchpriority (so it is auto).

I've addressed this in 1ab3c34.

And in core, I've addressed in WordPress/wordpress-develop#9770 via WordPress/wordpress-develop@e2d4676

…dd/script-module-fetchpriority-low

westonruter · 2025-09-05T23:08:46Z

@sirreal:

Script modules are registered with fetch priority. What if I enqueue a high fetch priority script that depends on a module registered with low? As the browser explores the dependency graph, will it determine that it should increase the priority of the dependency? Is that sort of priority dependence something that should be built into the core script modules system?

That's a great question. I put together a try-script-module-priorities plugin to test this.

The plugin registers three modules, foo, bar, baz. Module baz statically depends on bar, and bar statically depends on foo.

If baz has a fetchpriority of high but the static dependencies have a fetchpriority of low then this is the markup:

<script
  type="module"
  src="http://localhost:8000/wp-content/plugins/try-script-module-priorities/baz.js"
  id="baz-js-module"
  fetchpriority="high"
></script>
<link
  rel="modulepreload"
  href="http://localhost:8000/wp-content/plugins/try-script-module-priorities/bar.js"
  id="bar-js-modulepreload"
  fetchpriority="low"
/>
<link
  rel="modulepreload"
  href="http://localhost:8000/wp-content/plugins/try-script-module-priorities/foo.js"
  id="foo-js-modulepreload"
  fetchpriority="low"
/>

The result seems to be that the dependencies are not fetched with a high priority:

I see the same in Firefox and Safari.

It would be ideal that if a script module had a fetchpriority of high, that any dependent scripts would also get the same fetchpriority. This would be similar as was done for async/defer in WP_Scripts, but the key difference here is that there is not going to be any breakage caused by a differing priority. They all get executed once the DOM loads regardless.

This makes all the Gutenberg script modules low. That's fine at the moment. Have you considered how this system may evolve as more modules are introduced? What mechanism might modules have to report what fetch priority they should have?

For view script modules, this would be addressed by #71366. But for other utility script modules, I haven't filed an issue yet.

westonruter · 2025-09-06T02:13:58Z

It would be ideal that if a script module had a fetchpriority of high, that any dependent scripts would also get the same fetchpriority. This would be similar as was done for async/defer in WP_Scripts, but the key difference here is that there is not going to be any breakage caused by a differing priority. They all get executed once the DOM loads regardless.

See WordPress/wordpress-develop#9770

Co-authored-by: Jon Surrell <[email protected]>

* Add fetchpriority=low support to script modules * Update comment now that change landed in core * Add reference to related GB issue * Use multi-line comment Co-authored-by: westonruter <[email protected]> Co-authored-by: mukeshpanchal27 <[email protected]> Co-authored-by: sirreal <[email protected]> Co-authored-by: Mukesh Panchal <[email protected]> * Add comment explaining why a11y is fetchpriority=low Co-authored-by: Jon Surrell <[email protected]> --------- Co-authored-by: Mukesh Panchal <[email protected]> Co-authored-by: Jon Surrell <[email protected]>

* Allow scripts and script modules to be registered with a `fetchpriority` of `auto` (default), `high`, `low`: * When registering a script, add a `fetchpriority` arg to go alongside the `strategy` arg which was added for loading scripts with the `defer` and `async` loading strategies. See #12009. * For script modules, introduce an `$args` array parameter with a `fetchpriority` key to the `wp_register_script_module()`, and `wp_enqueue_script_module()` functions (and their respective underlying `WP_Script_Modules::register()` and `WP_Script_Modules::enqueue()` methods). This `$args` parameter corresponds with the same parameter used when registering non-module scripts. * Also for script modules, introduce `WP_Script_Modules::set_fetchpriority()` to override the `fetchpriority` for what was previously registered. * Emit a `_doing_it_wrong()` warning when an invalid `fetchpriority` value is used, and when `fetchpriority` is added to a script alias. * Include `fetchpriority` as an attribute on printed `SCRIPT` tags as well as on preload `LINK` tags for static script module dependencies. * Use a `fetchpriority` of `low` by default for: * Script modules used with the Interactivity API. For overriding this default in blocks, see [WordPress/gutenberg#71366 Gutenberg#71366]. * The `comment-reply` script. * Improve type checks and type hints. Developed in [WordPress#8815 GitHub PR], with [WordPress/gutenberg#70173 companion for Gutenberg]. Props westonruter, jonsurrell, swissspidy, luisherranz, kraftbj, audrasjb, dennysdionigi. Fixes #61734. git-svn-id: https://develop.svn.wordpress.org/trunk@60704 602fd350-edb4-49c9-b593-d223f7449a82

Add fetchpriority=low support to script modules

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westonruter mentioned this pull request May 21, 2025

Introduce fetchpriority for Scripts and Script Modules WordPress/wordpress-develop#8815

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Merge branch 'trunk' of https://github.com/WordPress/gutenberg into a…

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…dd/script-module-fetchpriority-low

westonruter marked this pull request as ready for review September 3, 2025 21:10

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Update comment now that change landed in core

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Add reference to related GB issue

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Use multi-line comment

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Co-authored-by: Mukesh Panchal <[email protected]>

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Merge branch 'trunk' of https://github.com/WordPress/gutenberg into a…

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…dd/script-module-fetchpriority-low

westonruter mentioned this pull request Sep 6, 2025

Script Loader: Bump fetchpriority for dependencies to be as high as recursive dependents for scripts and script modules WordPress/wordpress-develop#9770

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Add comment explaining why a11y is fetchpriority=low

1ab3c34

Co-authored-by: Jon Surrell <[email protected]>

westonruter requested a review from sirreal September 6, 2025 02:39

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westonruter merged commit ef6db07 into trunk Sep 8, 2025
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westonruter deleted the add/script-module-fetchpriority-low branch September 8, 2025 15:21

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maxschmeling mentioned this pull request Oct 7, 2025

Add BlockCanvasCover SlotFill #72119

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Add fetchpriority=low support to script modules #70173

Add fetchpriority=low support to script modules #70173

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