refactor(defaultTheme): refine keepFocusOnBackwardForward()

Author: marjune163

src/tpl/defaultTheme/frontend/index.js

@@ -161,10 +161,7 @@
 
 	function keepFocusOnBackwardForward() {
 		function onFocus(e) {
-			var link = e.target;
-			while (link && !(link instanceof HTMLAnchorElement)) {
-				link = link.parentElement;
-			}
+			var link = e.target.closest('a');
 			if (!link || link === lastFocused) return;
 			lastFocused = link;
 		}
@@ -1164,4 +1161,4 @@
 	enableKeyboardNavigate();
 	enhanceUpload();
 	enableNonRefreshDelete();
-})();
+}());