Stats: Deprioritize stats script with fetchpriority=low and remove dns-prefetch by kraftbj · Pull Request #47936 · Automattic/jetpack

kraftbj · 2026-04-03T15:57:27Z

Proposed changes

Add fetchpriority="low" to the Jetpack Stats script tag via the WP core wp_script_attributes filter, reducing network contention with LCP resources in Safari and Firefox (which don't automatically deprioritize async/defer scripts like Chrome does).
Remove the automatic dns-prefetch resource hint for stats.wp.com via the wp_resource_hints filter, since front-loading DNS resolution for a deliberately deprioritized resource is counterproductive.

Other information

This follows the approach from Weston Ruter's demo plugin and writeup. Uses the WP core wp_script_attributes filter (available since WP 6.1) instead of string-replacing on script_loader_tag.

Related product discussion/links

Linear: HOG-123

Does this pull request change what data or activity we track or use?

No. This only changes the priority/timing of the existing stats script loading — no changes to what is tracked.

Testing instructions

Activate Jetpack with Stats enabled on a test site.
Load a frontend page and inspect the HTML source.
Verify the jetpack-stats script tag includes fetchpriority="low".
Verify there is no <link rel="dns-prefetch" href="//stats.wp.com"> in the <head>.
Run the stats package unit tests: jp docker phpunit projects/packages/stats — all 105 tests should pass.

… filter Use the WP core wp_script_attributes filter to add fetchpriority=low to the jetpack-stats script tag. This reduces network contention with LCP resources in Safari and Firefox, which don't automatically deprioritize async/defer scripts. See HOG-123

Remove the automatic dns-prefetch resource hint for stats.wp.com since we're deprioritizing the stats script with fetchpriority=low. Front-loading DNS resolution for a deliberately delayed resource is counterproductive. See HOG-123

See HOG-123

github-actions · 2026-04-03T15:58:18Z

Are you an Automattician? Please test your changes on all WordPress.com environments to help mitigate accidental explosions.

To test on WoA, go to the Plugins menu on a WoA dev site. Click on the "Upload" button and follow the upgrade flow to be able to upload, install, and activate the Jetpack Beta plugin. Once the plugin is active, go to Jetpack > Jetpack Beta, select your plugin (Jetpack or WordPress.com Site Helper), and enable the enhance/stats-fetchpriority-low-HOG-123 branch.
To test on Simple, run the following command on your sandbox:

bin/jetpack-downloader test jetpack enhance/stats-fetchpriority-low-HOG-123

bin/jetpack-downloader test jetpack-mu-wpcom-plugin enhance/stats-fetchpriority-low-HOG-123

Interested in more tips and information?

In your local development environment, use the jetpack rsync command to sync your changes to a WoA dev blog.
Read more about our development workflow here: PCYsg-eg0-p2
Figure out when your changes will be shipped to customers here: PCYsg-eg5-p2

github-actions · 2026-04-03T15:58:32Z

Thank you for your PR!

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✅ Include a description of your PR changes.
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kraftbj · 2026-04-03T16:02:32Z

Note: The wp_resource_hints filter to remove the dns-prefetch for stats.wp.com is needed because wp_dependencies_unique_hosts() doesn't check fetchpriority data when building dns-prefetch hints — the two systems don't talk to each other yet. Weston flagged this as a TODO in his demo plugin (wp_dependencies_unique_hosts() could omit adding any resource hints for dependencies with low priority). Once core addresses that gap, our filter becomes a harmless no-op.

jp-launch-control · 2026-04-03T16:13:06Z

Code Coverage Summary

Coverage changed in 1 file.

File	Coverage	Δ%	Δ Uncovered
projects/packages/stats/src/class-tracking-pixel.php	100/132 (75.76%)	0.97%	2 ❤️‍🩹

Full summary · PHP report · JS report

Copilot

Pull request overview

This PR improves frontend performance for Jetpack Stats by lowering the network priority of the Stats script and avoiding an early DNS lookup that would work against that deprioritization.

Changes:

Add fetchpriority="low" to the jetpack-stats script tag via the wp_script_attributes filter.
Remove the automatic dns-prefetch hint for stats.wp.com via the wp_resource_hints filter.
Add unit tests for the new attribute/hint-filtering helpers and include a changelog fragment.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
projects/packages/stats/src/class-tracking-pixel.php	Adds the new filters to set low fetch priority on the Stats script and remove the `stats.wp.com` DNS prefetch hint.
projects/packages/stats/tests/php/Tracking_Pixel_Test.php	Adds tests covering the new helper callbacks for script attributes and resource hints.
projects/packages/stats/changelog/enhance-stats-fetchpriority-low-HOG-123	Documents the behavioral change in the Stats package changelog.

projects/packages/stats/src/class-tracking-pixel.php

Copilot · 2026-04-03T16:17:25Z

projects/packages/stats/tests/php/Tracking_Pixel_Test.php

+		$this->assertContains( '//stats.wp.com', $result );
+	}
+
 	/**


Current tests validate the helper callbacks directly, but they don't verify that enqueue_stats_script() actually registers the wp_script_attributes / wp_resource_hints filters. Adding an integration-style test that calls enqueue_stats_script() and asserts has_filter(...) (and/or runs apply_filters(...)) would prevent regressions where the new behavior is accidentally not hooked up.

Suggested change

/**

/**

* Test that enqueue_stats_script registers the expected filters and they run when applied.

*/

public function test_enqueue_stats_script_registers_filters() {

$tracking_pixel = new Tracking_Pixel();

remove_filter( 'wp_script_attributes', array( Tracking_Pixel::class, 'add_low_fetchpriority' ), 10 );

remove_filter( 'wp_resource_hints', array( Tracking_Pixel::class, 'remove_stats_dns_prefetch' ), 10 );

$tracking_pixel->enqueue_stats_script();

$this->assertNotFalse(

has_filter( 'wp_script_attributes', array( Tracking_Pixel::class, 'add_low_fetchpriority' ) )

);

$this->assertNotFalse(

has_filter( 'wp_resource_hints', array( Tracking_Pixel::class, 'remove_stats_dns_prefetch' ) )

);

$script_attributes = apply_filters(

'wp_script_attributes',

array(

'id' => 'jetpack-stats-js',

'src' => 'https://stats.wp.com/e-202445.js',

)

);

$this->assertSame( 'low', $script_attributes['fetchpriority'] );

$resource_hints = apply_filters(

'wp_resource_hints',

array( '//stats.wp.com', '//example.com' ),

'dns-prefetch'

);

$this->assertNotContains( '//stats.wp.com', $resource_hints );

$this->assertContains( '//example.com', $resource_hints );

remove_filter( 'wp_script_attributes', array( Tracking_Pixel::class, 'add_low_fetchpriority' ), 10 );

remove_filter( 'wp_resource_hints', array( Tracking_Pixel::class, 'remove_stats_dns_prefetch' ), 10 );

}

/**

projects/packages/stats/changelog/enhance-stats-fetchpriority-low-HOG-123

kraftbj added 3 commits April 3, 2026 10:47

Stats: Remove dns-prefetch for stats.wp.com

f4bb88b

Remove the automatic dns-prefetch resource hint for stats.wp.com since we're deprioritizing the stats script with fetchpriority=low. Front-loading DNS resolution for a deliberately delayed resource is counterproductive. See HOG-123

Stats: Add changelog for fetchpriority and dns-prefetch changes

3a339d6

See HOG-123

kraftbj added the [Status] Needs Review This PR is ready for review. label Apr 3, 2026

kraftbj self-assigned this Apr 3, 2026

kraftbj added the [Status] Needs Review This PR is ready for review. label Apr 3, 2026

github-actions bot added [Package] Stats Data [Tests] Includes Tests labels Apr 3, 2026

kraftbj requested a review from Copilot April 3, 2026 16:11

Copilot started reviewing on behalf of kraftbj April 3, 2026 16:12 View session

Copilot AI reviewed Apr 3, 2026

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Stats: Deprioritize stats script with fetchpriority=low and remove dns-prefetch#47936

Stats: Deprioritize stats script with fetchpriority=low and remove dns-prefetch#47936
kraftbj wants to merge 3 commits intotrunkfrom
enhance/stats-fetchpriority-low-HOG-123

kraftbj commented Apr 3, 2026

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-	/**
+	/**
+	 * Test that enqueue_stats_script registers the expected filters and they run when applied.
+	 */
+	public function test_enqueue_stats_script_registers_filters() {
+		$tracking_pixel = new Tracking_Pixel();
+		remove_filter( 'wp_script_attributes', array( Tracking_Pixel::class, 'add_low_fetchpriority' ), 10 );
+		remove_filter( 'wp_resource_hints', array( Tracking_Pixel::class, 'remove_stats_dns_prefetch' ), 10 );
+		$tracking_pixel->enqueue_stats_script();
+		$this->assertNotFalse(
+			has_filter( 'wp_script_attributes', array( Tracking_Pixel::class, 'add_low_fetchpriority' ) )
+		);
+		$this->assertNotFalse(
+			has_filter( 'wp_resource_hints', array( Tracking_Pixel::class, 'remove_stats_dns_prefetch' ) )
+		);
+		$script_attributes = apply_filters(
+			'wp_script_attributes',
+			array(
+				'id'  => 'jetpack-stats-js',
+				'src' => 'https://stats.wp.com/e-202445.js',
+			)
+		);
+		$this->assertSame( 'low', $script_attributes['fetchpriority'] );
+		$resource_hints = apply_filters(
+			'wp_resource_hints',
+			array( '//stats.wp.com', '//example.com' ),
+			'dns-prefetch'
+		);
+		$this->assertNotContains( '//stats.wp.com', $resource_hints );
+		$this->assertContains( '//example.com', $resource_hints );
+		remove_filter( 'wp_script_attributes', array( Tracking_Pixel::class, 'add_low_fetchpriority' ), 10 );
+		remove_filter( 'wp_resource_hints', array( Tracking_Pixel::class, 'remove_stats_dns_prefetch' ), 10 );
+	}
+	/**

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kraftbj commented Apr 3, 2026

Proposed changes

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Does this pull request change what data or activity we track or use?

Testing instructions

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