refactor(defaultTheme): refine keepFocusOnBackwardForward()

Author: marjune163

src/tpl/defaultTheme/frontend/index.js

@@ -154,10 +154,13 @@
 
 	function keepFocusOnBackwardForward() {
 		function onFocus(e) {
-			var link = e.target;
-			while (link && !(link instanceof HTMLAnchorElement)) {
-				link = link.parentElement;
-			}
+			var link = e.target.closest ? e.target.closest('a') : (function () {
+				var anchor = e.target;
+				while (anchor && !(anchor instanceof HTMLAnchorElement)) {
+					anchor = anchor.parentElement;
+				}
+				return anchor;
+			}())
 			if (!link || link === lastFocused) return;
 			lastFocused = link;
 		}
@@ -1157,4 +1160,4 @@
 	enableKeyboardNavigate();
 	enhanceUpload();
 	enableNonRefreshDelete();
-})();
+}());