Reclaiming another 700-800 msecs on the 400 listview item test for WP7.5 (Mango) with a few minor tweaks:

- Added _findFirstElementByTagName() which does basic DOM traversal to find the first of an element with the given nodeName. Use this in place of $.fn.closest() and $.fn.children() calls that filter with ":eq(0)".
- Avoid calling $.fn.add() if you can. The creation of the new collection is costing about 400 msecs.
- Avoid calling $() with markup for a single node, just use document.createElement() and pass it to $().

Author: jblas

js/jquery.mobile.listview.js

@@ -92,6 +92,42 @@ $.widget( "mobile.listview", $.mobile.widget, {
 		}
 	},
 
+	// This is a generic utility method for finding the first
+	// node with a given nodeName. It uses basic DOM traversal
+	// to be fast and is meant to be a substitute for simple
+	// $.fn.closest() and $.fn.children() calls on a single
+	// element. Note that callers must pass both the lowerCase
+	// and upperCase version of the nodeName they are looking for.
+	// The main reason for this is that this function will be
+	// called many times and we want to avoid having to lowercase
+	// the nodeName from the element every time to ensure we have
+	// a match. Note that this function lives here for now, but may
+	// be moved into $.mobile if other components need a similar method.
+	_findFirstElementByTagName: function( ele, nextProp, lcName, ucName )
+	{
+		var dict = {};
+		dict[ lcName ] = dict[ ucName ] = true;
+		while ( ele ) {
+			if ( dict[ ele.nodeName ] ) {
+				return ele;
+			}
+			ele = ele[ nextProp ];
+		}
+		return null;
+	},
+	
+	_addThumbClasses: function( containers )
+	{
+		var i, img, len = containers.length;
+		for ( i = 0; i < len; i++ ) {
+			img = $( this._findFirstElementByTagName( containers[ i ].firstChild, "nextSibling", "img", "IMG" ) );
+			if ( img.length ) {
+				img.addClass( "ui-li-thumb" );
+				$( this._findFirstElementByTagName( img[ 0 ].parentNode, "parentNode", "li", "LI" ) ).addClass( img.is( ".ui-li-icon" ) ? "ui-li-has-icon" : "ui-li-has-thumb" );
+			}
+		}
+	},
+
 	refresh: function( create ) {
 		this.parentPage = this.element.closest( ".ui-page" );
 		this._createSubPages();
@@ -157,7 +193,7 @@ $.widget( "mobile.listview", $.mobile.widget, {
 							})
 							.find( ".ui-btn-inner" )
 								.append(
-									$( "<span />" ).buttonMarkup({
+									$( document.createElement( "span" ) ).buttonMarkup({
 										shadow: true,
 										corners: true,
 										theme: splittheme,
@@ -188,7 +224,7 @@ $.widget( "mobile.listview", $.mobile.widget, {
 					.prepend( "<span class='ui-li-dec'>" + (counter++) + ". </span>" );
 			}
 
-			item.add( item.children( ".ui-btn-inner" ) ).addClass( itemClass );
+			item.addClass( itemClass ).children( ".ui-btn-inner" ).addClass( itemClass );
 		}
 
 		$list.find( "h1, h2, h3, h4, h5, h6" ).addClass( "ui-li-heading" )
@@ -219,14 +255,8 @@ $.widget( "mobile.listview", $.mobile.widget, {
 		// allows the 400 listview item page to load in about 3 seconds as
 		// opposed to 30 seconds.
 
-		imgParents = li.add( $list.find( ".ui-link-inherit" ) );
-
-		for ( pos = 0; pos < imgParents.length; pos++ ) {
-			img = imgParents.eq( pos ).children( "img" ).first();
-			if ( img.length ) {
-				img.addClass( "ui-li-thumb" ).closest( "li" ).addClass( img.is( ".ui-li-icon" ) ? "ui-li-has-icon" : "ui-li-has-thumb" );
-			}
-		}
+		this._addThumbClasses( li );
+		this._addThumbClasses( $list.find( ".ui-link-inherit" ) );
 
 		this._refreshCorners( create );
 	},