CSS: Skip falsy values in `addClass( array )`, compress code

This change makes jQuery skip falsy values in `addClass( array )`
& `removeClass( array )` instead of stopping iteration when the first falsy
value is detected. This makes code like:
```js
elem.addClass( [ "a", "", "b" ] );
```
add both the `a` & `b` classes.

The code was also optimized for size a bit so it doesn't increase the
minified gzipped size.

Fixes gh-4998
Closes gh-5003

(partially cherry picked from commit a338b407f2479f82df40635055effc163835183f)

1 files changed, 38 insertions, 0 deletions

diff --git a/test/unit/attributes.js b/test/unit/attributes.js
index caec5c8c5..787dd3a02 100644
--- a/test/unit/attributes.js
+++ b/test/unit/attributes.js
@@ -1631,6 +1631,44 @@ QUnit.test( "addClass, removeClass, hasClass on elements with classes with non-H
 	testMatches();
 } );
 
+( function() {
+	var rnothtmlwhite = /[^\x20\t\r\n\f]+/g;
+
+	function expectClasses( assert, elem, classes ) {
+		var actualClassesSorted = ( elem.attr( "class" ).match( rnothtmlwhite ) || [] )
+			.sort().join( " " );
+		var classesSorted = classes.slice()
+			.sort().join( " " );
+		assert.equal( actualClassesSorted, classesSorted, "Expected classes present" );
+	}
+
+	QUnit.test( "addClass on arrays with falsy elements (gh-4998)", function( assert ) {
+		assert.expect( 3 );
+
+		var elem = jQuery( "<div class='a'></div>" );
+
+		elem.addClass( [ "b", "", "c" ] );
+		expectClasses( assert, elem, [ "a", "b", "c" ] );
+		elem.addClass( [ "", "d" ] );
+		expectClasses( assert, elem, [ "a", "b", "c", "d" ] );
+		elem.addClass( [ "e", "" ] );
+		expectClasses( assert, elem, [ "a", "b", "c", "d", "e" ] );
+	} );
+
+	QUnit.test( "removeClass on arrays with falsy elements (gh-4998)", function( assert ) {
+		assert.expect( 3 );
+
+		var elem = jQuery( "<div class='a b c d e'></div>" );
+
+		elem.removeClass( [ "e", "" ] );
+		expectClasses( assert, elem, [ "a", "b", "c", "d" ] );
+		elem.removeClass( [ "", "d" ] );
+		expectClasses( assert, elem, [ "a", "b", "c" ] );
+		elem.removeClass( [ "b", "", "c" ] );
+		expectClasses( assert, elem, [ "a" ] );
+	} );
+} )();
+
 QUnit.test( "contents().hasClass() returns correct values", function( assert ) {
 	assert.expect( 2 );