Slider: Prevent the default action on keydown if we're listening for …

…the pressed key. Fixes #8109 - Slider: Key handling should prevent scrolling.

(cherry picked from commit 0434bce)

ui/jquery.ui.slider.js

@@ -115,8 +115,7 @@ $.widget( "ui.slider", $.ui.mouse, {
 
 		this.handles
 			.keydown(function( event ) {
-				var ret = true,
-					index = $( this ).data( "index.ui-slider-handle" ),
+				var index = $( this ).data( "index.ui-slider-handle" ),
 					allowed,
 					curVal,
 					newVal,
@@ -135,7 +134,7 @@ $.widget( "ui.slider", $.ui.mouse, {
 					case $.ui.keyCode.RIGHT:
 					case $.ui.keyCode.DOWN:
 					case $.ui.keyCode.LEFT:
-						ret = false;
+						event.preventDefault();
 						if ( !self._keySliding ) {
 							self._keySliding = true;
 							$( this ).addClass( "ui-state-active" );
@@ -184,9 +183,6 @@ $.widget( "ui.slider", $.ui.mouse, {
 				}
 
 				self._slide( event, index, newVal );
-
-				return ret;
-
 			})
 			.keyup(function( event ) {
 				var index = $( this ).data( "index.ui-slider-handle" );