Widget: Optimize attachment of the _untrackClassesElement listener

jQuery UI 1.13.0 changed the logic attaching the `_untrackClassesElement`
listener in the `_classes` widget method; one of the side effects was calling
`this._on` for each node that needed the listener. That caused a severe
performance degradation for large comboboxes as each `_on` jQuery UI call
causes a jQuery `add` call that calls Sizzle's `uniqueSort` underneath.

Instead, collect the nodes that need the listener and then, outside of the loop,
create a jQuery object out of them and attach the listener once. That's still
slower than the jQuery 1.12 version but only slightly: 936 ms to 1.03s on a very
large list on a recent MacBook Pro, compared to ~30 seconds before this patch.

Fixes gh-2014
Closes gh-2037

1 files changed, 23 insertions, 0 deletions

diff --git a/tests/unit/autocomplete/core.js b/tests/unit/autocomplete/core.js
index a2a36cb4c..2083e16b1 100644
--- a/tests/unit/autocomplete/core.js
+++ b/tests/unit/autocomplete/core.js
@@ -443,4 +443,27 @@ QUnit.test( "Close on click outside when focus remains", function( assert ) {
 	} );
 } );
 
+QUnit.test( "extra listeners created during typing (trac-15082, trac-15095)", function( assert ) {
+	assert.expect( 2 );
+
+	var origRemoveListenersCount;
+	var element = $( "#autocomplete" ).autocomplete( {
+		source: [ "java", "javascript" ],
+		delay: 0
+	} );
+
+	element.val( "j" ).autocomplete( "search", "j" );
+	origRemoveListenersCount = jQuery._data( element[ 0 ], "events" ).remove.length;
+
+	element.val( "ja" ).autocomplete( "search", "ja" );
+	assert.equal( jQuery._data( element[ 0 ], "events" ).remove.length,
+		origRemoveListenersCount,
+		"No extra listeners after typing multiple letters" );
+
+	element.val( "jav" ).autocomplete( "search", "jav" );
+	assert.equal( jQuery._data( element[ 0 ], "events" ).remove.length,
+		origRemoveListenersCount,
+		"No extra listeners after typing multiple letters" );
+} );
+
 } );