Index: src/js/_enqueues/lib/nav-menu.js
===================================================================
--- src/js/_enqueues/lib/nav-menu.js	(revision 44648)
+++ src/js/_enqueues/lib/nav-menu.js	(working copy)
@@ -835,6 +835,20 @@
 					}
 				}
 			});
+
+			$( '#menu-name' ).on( 'input', _.debounce( function () {
+				var menuName = $( document.getElementById( 'menu-name' ) ),
+					menuNameVal = menuName.val();
+
+				if ( ! menuNameVal || ! menuNameVal.replace( /\s+/, '' ) ) {
+					// Add warning for invalid menu name.
+					menuName.parent().addClass( 'form-invalid' );
+				} else {
+					// Remove warning for valid menu name.
+					menuName.parent().removeClass( 'form-invalid' );
+				}
+			}, 500 ) );
+
 			$('#add-custom-links input[type="text"]').keypress(function(e){
 				$('#customlinkdiv').removeClass('form-invalid');
 
@@ -1166,8 +1180,8 @@
 			menuName = $('#menu-name'),
 			menuNameVal = menuName.val();
 			// Cancel and warn if invalid menu name
-			if( !menuNameVal || menuNameVal == menuName.attr('title') || !menuNameVal.replace(/\s+/, '') ) {
-				menuName.parent().addClass('form-invalid');
+			if ( ! menuNameVal || ! menuNameVal.replace( /\s+/, '' ) ) {
+				menuName.parent().addClass( 'form-invalid' );
 				return false;
 			}
 			// Copy menu theme locations
Index: src/wp-includes/script-loader.php
===================================================================
--- src/wp-includes/script-loader.php	(revision 44648)
+++ src/wp-includes/script-loader.php	(working copy)
@@ -1779,8 +1779,11 @@
 			)
 		);
 
-		// Navigation Menus
-		$scripts->add( 'nav-menu', "/wp-admin/js/nav-menu$suffix.js", array( 'jquery-ui-sortable', 'jquery-ui-draggable', 'jquery-ui-droppable', 'wp-lists', 'postbox', 'json2' ) );
+		/*
+		 * Navigation Menus: Adding underscore as a dependency to utilize _.debounce
+		 * see https://core.trac.wordpress.org/ticket/42321
+		 */
+		$scripts->add( 'nav-menu', "/wp-admin/js/nav-menu$suffix.js", array( 'jquery-ui-sortable', 'jquery-ui-draggable', 'jquery-ui-droppable', 'wp-lists', 'postbox', 'json2', 'underscore' ) );
 		did_action( 'init' ) && $scripts->localize(
 			'nav-menu',
 			'navMenuL10n',