Index: src/wp-admin/js/nav-menu.js
===================================================================
--- src/wp-admin/js/nav-menu.js	(revision 42022)
+++ src/wp-admin/js/nav-menu.js	(working copy)
@@ -829,6 +829,17 @@
 					}
 				}
 			});
+			$( '#menu-name' ).on('keyup', _.debounce(function (e) {
+				menuName = $( document.getElementById( 'menu-name' ) ),
+			    menuNameVal = menuName.val();
+				if ( !menuNameVal || menuNameVal == menuName.attr('title') || !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');
 
Index: src/wp-admin/nav-menus.php
===================================================================
--- src/wp-admin/nav-menus.php	(revision 42022)
+++ src/wp-admin/nav-menus.php	(working copy)
@@ -27,6 +27,7 @@
 	);
 }
 
+wp_enqueue_script( 'underscore' );
 wp_enqueue_script( 'nav-menu' );
 
 if ( wp_is_mobile() )