Widget: Properly set widgetEventPrefix when redefining a widget. Fixe…

…s #9316 - Widget: widgetEventPrefix is empty when widget is (occasionally) loaded twice.

(cherry picked from commit 2eb89f0)

tests/unit/widget/widget_core.js

@@ -331,6 +331,16 @@ test( "re-init", function() {
 	deepEqual( actions, [ "optionfoo", "init" ], "correct methods called on re-init with options" );
 });
 
+test( "redeclare", function() {
+	expect( 2 );
+
+	$.widget( "ui.testWidget", {} );
+	equal( $.ui.testWidget.prototype.widgetEventPrefix, "testWidget" );
+
+	$.widget( "ui.testWidget", {} );
+	equal( $.ui.testWidget.prototype.widgetEventPrefix, "testWidget" );
+});
+
 test( "inheritance", function() {
 	expect( 6 );
 	// #5830 - Widget: Using inheritance overwrites the base classes options

ui/jquery.ui.widget.js

@@ -106,7 +106,7 @@ $.widget = function( name, base, prototype ) {
 		// TODO: remove support for widgetEventPrefix
 		// always use the name + a colon as the prefix, e.g., draggable:start
 		// don't prefix for widgets that aren't DOM-based
-		widgetEventPrefix: existingConstructor ? basePrototype.widgetEventPrefix : name
+		widgetEventPrefix: existingConstructor ? (basePrototype.widgetEventPrefix || name) : name
 	}, proxiedPrototype, {
 		constructor: constructor,
 		namespace: namespace,