Rewrote .merge() (faster and less obtuse now). Fixed #5610.

src/core.js

@@ -567,23 +567,20 @@ jQuery.extend({
 	},
 
 	merge: function( first, second ) {
-		var pos, i = second.length;
+		var i = first.length, j = 0;
 
-		// We have to get length this way when IE & Opera overwrite the length
-		// expando of getElementsByTagName
-		if ( i && i.nodeType ) {
-			for ( i = 0; second[i]; ++i ) {}
-		}
-
-		pos = i + first.length;
-
-		// Correct length for non Arrays
-		first.length = pos;
-
-		while ( i ) {
-			first[ --pos ] = second[ --i ];
+		if ( typeof second.length === "number" ) {
+			for ( var l = second.length; j < l; j++ ) {
+				first[ i++ ] = second[ j ];
+			}
+		} else {
+			while ( second[j] !== undefined ) {
+				first[ i++ ] = second[ j++ ];
+			}
 		}
 
+		first.length = i;
+
 		return first;
 	},
 

test/unit/core.js

@@ -711,7 +711,7 @@ test("jQuery.each(Object,Function)", function() {
 });
 
 test("jQuery.makeArray", function(){
-	expect(15);
+	expect(17);
 
 	equals( jQuery.makeArray(jQuery('html>*'))[0].nodeName.toUpperCase(), "HEAD", "Pass makeArray a jQuery object" );
 
@@ -744,6 +744,10 @@ test("jQuery.makeArray", function(){
 	equals( jQuery.makeArray(/a/)[0].constructor, RegExp, "Pass makeArray a regex" );
 
 	ok( jQuery.makeArray(document.getElementById('form')).length >= 13, "Pass makeArray a form (treat as elements)" );
+
+	// For #5610
+	same( jQuery.makeArray({'length': '0'}), [], "Make sure object is coerced properly.");
+	same( jQuery.makeArray({'length': '5'}), [], "Make sure object is coerced properly.");
 });
 
 test("jQuery.isEmptyObject", function(){