All: Remove usage of jQuery positional selectors

jQuery positional selectors () have been deprecated in
[jQuery 3.4.0](https://blog.jquery.com/2019/04/10/jquery-3-4-0-released/)
and they'll be removed in jQuery 4.0.0. This PR removes their usage.

Most of the changes were possible without changing public API. However,
dropping `:even` usage required a change to the
[`header` option](https://api.jqueryui.com/accordion/#option-header)
of the accordion widget. I made it an optional function; this will need
to be documented.

The polyfill for `.even()` & `.odd()` is added for jQuery <3.5.0. There was
no usage of the :odd selector in the code but the `.odd()` method is also
polyfilled for completeness.

Closes gh-1904

4 files changed, 28 insertions, 5 deletions

diff --git a/ui/jquery-1-7.js b/ui/jquery-1-7.js
index 5e7907a15..3d0870f7c 100644
--- a/ui/jquery-1-7.js
+++ b/ui/jquery-1-7.js
@@ -98,4 +98,21 @@ if ( !$.uniqueSort ) {
 	$.uniqueSort = $.unique;
 }
 
+// Support: jQuery 3.4.x or older
+// These methods have been defined in jQuery 3.5.0.
+if ( !$.fn.even || !$.fn.odd ) {
+	$.fn.extend( {
+		even: function() {
+			return this.filter( function( i ) {
+				return i % 2 === 0;
+			} );
+		},
+		odd: function() {
+			return this.filter( function( i ) {
+				return i % 2 === 1;
+			} );
+		}
+	} );
+}
+
 } ) );
diff --git a/ui/widgets/accordion.js b/ui/widgets/accordion.js
index 530d73543..59a6a7315 100644
--- a/ui/widgets/accordion.js
+++ b/ui/widgets/accordion.js
@@ -48,7 +48,9 @@ return $.widget( "ui.accordion", {
 		},
 		collapsible: false,
 		event: "click",
-		header: "> li > :first-child, > :not(li):even",
+		header: function( elem ) {
+			return elem.find( "> li > :first-child" ).add( elem.find( "> :not(li)" ).even() );
+		},
 		heightStyle: "auto",
 		icons: {
 			activeHeader: "ui-icon-triangle-1-s",
@@ -279,7 +281,11 @@ return $.widget( "ui.accordion", {
 		var prevHeaders = this.headers,
 			prevPanels = this.panels;
 
-		this.headers = this.element.find( this.options.header );
+		if ( typeof this.options.header === "function" ) {
+			this.headers = this.options.header( this.element );
+		} else {
+			this.headers = this.element.find( this.options.header );
+		}
 		this._addClass( this.headers, "ui-accordion-header ui-accordion-header-collapsed",
 			"ui-state-default" );
 
diff --git a/ui/widgets/datepicker.js b/ui/widgets/datepicker.js
index c777a4b0e..5e6321e1d 100644
--- a/ui/widgets/datepicker.js
+++ b/ui/widgets/datepicker.js
@@ -858,7 +858,7 @@ $.extend( Datepicker.prototype, {
 
 				//assure that inst.yearshtml didn't change.
 				if ( origyearshtml === inst.yearshtml && inst.yearshtml ) {
-					inst.dpDiv.find( "select.ui-datepicker-year:first" ).replaceWith( inst.yearshtml );
+					inst.dpDiv.find( "select.ui-datepicker-year" ).first().replaceWith( inst.yearshtml );
 				}
 				origyearshtml = inst.yearshtml = null;
 			}, 0 );
diff --git a/ui/widgets/dialog.js b/ui/widgets/dialog.js
index e4798e0d7..c9feee48a 100644
--- a/ui/widgets/dialog.js
+++ b/ui/widgets/dialog.js
@@ -369,8 +369,8 @@ $.widget( "ui.dialog", {
 					return;
 				}
 				var tabbables = this.uiDialog.find( ":tabbable" ),
-					first = tabbables.filter( ":first" ),
-					last = tabbables.filter( ":last" );
+					first = tabbables.first(),
+					last = tabbables.last();
 
 				if ( ( event.target === last[ 0 ] || event.target === this.uiDialog[ 0 ] ) &&
 						!event.shiftKey ) {