Improve speed of $.map with object support (-5% previous speed) and improve .length detection

src/core.js

@@ -704,16 +704,15 @@ jQuery.extend({
 		return ret;
 	},
 
-		// arg is for internal usage only
+	// arg is for internal usage only
 	map: function( elems, callback, arg ) {
 		var value, ret = [],
-			i = 0,		
+			i = 0,
 			length = elems.length,
-			// process .length if it's just an object member
-			isArray = length !== undefined && ( elems[ length - 1 ] || jQuery.isArray( elems ) );
-		
+			// jquery objects are treated as arrays
+			isArray = elems instanceof jQuery || length !== undefined && typeof length === "number" && ( ( length > 0 && elems[ 0 ] && elems[ length -1 ] ) || jQuery.isArray( elems ) ) ;
+
 		// Go through the array, translating each of the items to their
-		// new value (or values).
 		if ( isArray ) {
 			for ( ; i < length; i++ ) {
 				value = callback( elems[ i ], i, arg );
@@ -723,8 +722,8 @@ jQuery.extend({
 				}
 			}
 
-		// Go thorugh every key on the object, 
-		} else {		
+		// Go thorugh every key on the object,
+		} else {
 			for ( key in elems ) {
 				value = callback( elems[ key ], key, arg );
 

test/unit/core.js

@@ -625,7 +625,7 @@ test("map()", function() {
 		q("ap","ap","ap"),
 		"Single Map"
 	);
-	
+
 	//for #2616
 	var keys = jQuery.map( {a:1,b:2}, function( v, k ){
 		return k;
@@ -636,7 +636,7 @@ test("map()", function() {
 		return v;
 	});
 	equals( values.join(""), "12", "Map the values from a hash to an array" );
-	
+
 	// object with length prop
 	var values = jQuery.map( {a:1,b:2, length:3}, function( v, k ){
 		return v;