Fix for the Jetpack gallery exit back button returning to gallery instead of moving back in history

fix-jetpack-gallery-exit-history-back-issue.js

(function( $ ) {
	// This script needs the 'hashchange' event to work
	if ( 'undefined' === typeof window.onhashchange ) {
		return;
	}

	var historyLengthBeforeGallery = 0;

	// Catch the first hash change, ie: when the first slide opens
	jQuery( window ).on( 'hashchange', function() {
		if ( ! historyLengthBeforeGallery ) {
			historyLengthBeforeGallery = history.length - 1; // 1 here is the new page recorded on the opening slide
		}
	} );

	// Restore the history back in time before the gallery's first slide opened
	jQuery( document ).on( 'jp_carousel.afterClose', function() {
		history.go( historyLengthBeforeGallery - history.length )
	} );
})( jQuery );