Dialog: Only bind focus-trapping event once. Fixes #8551 - After repe…

…ated opening and closing of a modal dialog, focus navigation using tab becomes slow.

ui/jquery.ui.dialog.js

@@ -170,6 +170,25 @@ $.widget("ui.dialog", {
 		if ( $.fn.bgiframe ) {
 			uiDialog.bgiframe();
 		}
+
+		// prevent tabbing out of modal dialogs
+		this._on( uiDialog, { keydown: function( event ) {
+			if ( !options.modal || event.keyCode !== $.ui.keyCode.TAB ) {
+				return;
+			}
+
+			var tabbables = $( ":tabbable", uiDialog ),
+				first = tabbables.filter( ":first" ),
+				last  = tabbables.filter( ":last" );
+
+			if ( event.target === last[0] && !event.shiftKey ) {
+				first.focus( 1 );
+				return false;
+			} else if ( event.target === first[0] && event.shiftKey ) {
+				last.focus( 1 );
+				return false;
+			}
+		}});
 	},
 
 	_init: function() {
@@ -225,7 +244,6 @@ $.widget("ui.dialog", {
 		if ( this.overlay ) {
 			this.overlay.destroy();
 		}
-		this._off( this.uiDialog, "keypress" );
 
 		if ( this.options.hide ) {
 			this.uiDialog.hide( this.options.hide, function() {
@@ -309,27 +327,6 @@ $.widget("ui.dialog", {
 		this.overlay = options.modal ? new $.ui.dialog.overlay( this ) : null;
 		this.moveToTop( true );
 
-		// prevent tabbing out of modal dialogs
-		if ( options.modal ) {
-			this._on( uiDialog, { keydown: function( event ) {
-				if ( event.keyCode !== $.ui.keyCode.TAB ) {
-					return;
-				}
-
-				var tabbables = $( ":tabbable", uiDialog ),
-					first = tabbables.filter( ":first" ),
-					last  = tabbables.filter( ":last" );
-
-				if ( event.target === last[0] && !event.shiftKey ) {
-					first.focus( 1 );
-					return false;
-				} else if ( event.target === first[0] && event.shiftKey ) {
-					last.focus( 1 );
-					return false;
-				}
-			}});
-		}
-
 		// set focus to the first tabbable element in the content area or the first button
 		// if there are no tabbable elements, set focus on the dialog itself
 		hasFocus = this.element.find( ":tabbable" );