try-slow-events.php

<?php
/**
 * Plugin Name: Try Slow Click Event Directives
 * Plugin URI: https://gist.github.com/westonruter/59f7c58230bd5d1e82733e5b87d245dc
 * Description: Testing 
 * Requires at least: 6.5
 * Requires PHP: 7.2
 * Version: 0.1.0
 * Author: Weston Ruter
 * Update URI: https://gist.github.com/westonruter/59f7c58230bd5d1e82733e5b87d245dc
 */
if ( ! isset( $_GET['try-slow-events'] ) ) {
	return;
}

add_action(
	'wp_enqueue_scripts',
	static function () {
		wp_register_script_module( 'try-slow-events', plugin_dir_url( __FILE__ ) . 'view.js' );
	}
);

add_filter(
	'render_block_core/image',
	static function ( $block_content ) {
		wp_enqueue_script_module( 'try-slow-events' );

		$directive = $_GET['try-slow-events'] === 'async' ? 'data-wp-on-async' : 'data-wp-on';

		$p = new WP_HTML_Tag_Processor( $block_content );
		while ( $p->next_tag( array( 'tag_name' => 'IMG' ) ) ) {
			for ( $i = 1; $i <= 10; $i++ ) {
				$p->set_attribute( "$directive--click--slow-event-$i", 'trySlowEvents::actions.doFortyFiveMillisecondsOfWork' );
			}
		}
		return $p->get_updated_html();
	}
);

view.js

import { store } from '@wordpress/interactivity';

console.info( 'Testing Slow Event Directives' );

function doWork( ms ) {
	const startTime = performance.now();
	while ( performance.now() - startTime < ms ) {}
}

function doFortyFiveMillisecondsOfWork() {
	doWork( 45 );
}

store( 'trySlowEvents', {
	actions: {
		doFortyFiveMillisecondsOfWork
	}
} );