Add "select all" option inside the PMPro Require Membership box

my_add_select_all_levels.php

<?php
/**
 * Add "select all" option inside the Require Membership box
 * You can add this recipe to your site by creating a custom plugin
 * or using the Code Snippets plugin available for free in the WordPress repository.
 * Read this companion article for step-by-step directions on either method.
 * https://www.paidmembershipspro.com/create-a-plugin-for-pmpro-customizations/
 */
function my_add_select_all_levels() {
?>
<script>
	jQuery(document).ready(function() {
		var my_sal_toggle = true;
		jQuery('#membershipschecklist').before('<a href="javascript:void();" id="my_pmpro_select_all_levels">select all</a>');
		jQuery('#my_pmpro_select_all_levels').click(function(){
			jQuery('#membershipschecklist input').prop('checked', my_sal_toggle);
			my_sal_toggle = ! my_sal_toggle;
		});
	});	
</script>
<?php	
}
add_action( 'pmpro_after_require_membership_metabox', 'my_add_select_all_levels' );