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 a338b40)

src/attributes/classes.js

@@ -25,45 +25,43 @@ function classesToArray( value ) {
 
 jQuery.fn.extend( {
 	addClass: function( value ) {
-		var classes, elem, cur, curValue, clazz, j, finalValue,
-			i = 0;
+		var classNames, cur, curValue, className, i, finalValue;
 
 		if ( isFunction( value ) ) {
 			return this.each( function( j ) {
 				jQuery( this ).addClass( value.call( this, j, getClass( this ) ) );
 			} );
 		}
 
-		classes = classesToArray( value );
+		classNames = classesToArray( value );
 
-		if ( classes.length ) {
-			while ( ( elem = this[ i++ ] ) ) {
-				curValue = getClass( elem );
-				cur = elem.nodeType === 1 && ( " " + stripAndCollapse( curValue ) + " " );
+		if ( classNames.length ) {
+			return this.each( function() {
+				curValue = getClass( this );
+				cur = this.nodeType === 1 && ( " " + stripAndCollapse( curValue ) + " " );
 
 				if ( cur ) {
-					j = 0;
-					while ( ( clazz = classes[ j++ ] ) ) {
-						if ( cur.indexOf( " " + clazz + " " ) < 0 ) {
-							cur += clazz + " ";
+					for ( i = 0; i < classNames.length; i++ ) {
+						className = classNames[ i ];
+						if ( cur.indexOf( " " + className + " " ) < 0 ) {
+							cur += className + " ";
 						}
 					}
 
 					// Only assign if different to avoid unneeded rendering.
 					finalValue = stripAndCollapse( cur );
 					if ( curValue !== finalValue ) {
-						elem.setAttribute( "class", finalValue );
+						this.setAttribute( "class", finalValue );
 					}
 				}
-			}
+			} );
 		}
 
 		return this;
 	},
 
 	removeClass: function( value ) {
-		var classes, elem, cur, curValue, clazz, j, finalValue,
-			i = 0;
+		var classNames, cur, curValue, className, i, finalValue;
 
 		if ( isFunction( value ) ) {
 			return this.each( function( j ) {
@@ -75,45 +73,42 @@ jQuery.fn.extend( {
 			return this.attr( "class", "" );
 		}
 
-		classes = classesToArray( value );
+		classNames = classesToArray( value );
 
-		if ( classes.length ) {
-			while ( ( elem = this[ i++ ] ) ) {
-				curValue = getClass( elem );
+		if ( classNames.length ) {
+			return this.each( function() {
+				curValue = getClass( this );
 
 				// This expression is here for better compressibility (see addClass)
-				cur = elem.nodeType === 1 && ( " " + stripAndCollapse( curValue ) + " " );
+				cur = this.nodeType === 1 && ( " " + stripAndCollapse( curValue ) + " " );
 
 				if ( cur ) {
-					j = 0;
-					while ( ( clazz = classes[ j++ ] ) ) {
+					for ( i = 0; i < classNames.length; i++ ) {
+						className = classNames[ i ];
 
 						// Remove *all* instances
-						while ( cur.indexOf( " " + clazz + " " ) > -1 ) {
-							cur = cur.replace( " " + clazz + " ", " " );
+						while ( cur.indexOf( " " + className + " " ) > -1 ) {
+							cur = cur.replace( " " + className + " ", " " );
 						}
 					}
 
 					// Only assign if different to avoid unneeded rendering.
 					finalValue = stripAndCollapse( cur );
 					if ( curValue !== finalValue ) {
-						elem.setAttribute( "class", finalValue );
+						this.setAttribute( "class", finalValue );
 					}
 				}
-			}
+			} );
 		}
 
 		return this;
 	},
 
 	toggleClass: function( value, stateVal ) {
-		var type = typeof value,
+		var classNames, className, i, self,
+			type = typeof value,
 			isValidValue = type === "string" || Array.isArray( value );
 
-		if ( typeof stateVal === "boolean" && isValidValue ) {
-			return stateVal ? this.addClass( value ) : this.removeClass( value );
-		}
-
 		if ( isFunction( value ) ) {
 			return this.each( function( i ) {
 				jQuery( this ).toggleClass(
@@ -123,17 +118,20 @@ jQuery.fn.extend( {
 			} );
 		}
 
-		return this.each( function() {
-			var className, i, self, classNames;
+		if ( typeof stateVal === "boolean" && isValidValue ) {
+			return stateVal ? this.addClass( value ) : this.removeClass( value );
+		}
 
+		classNames = classesToArray( value );
+
+		return this.each( function() {
 			if ( isValidValue ) {
 
 				// Toggle individual class names
-				i = 0;
 				self = jQuery( this );
-				classNames = classesToArray( value );
 
-				while ( ( className = classNames[ i++ ] ) ) {
+				for ( i = 0; i < classNames.length; i++ ) {
+					className = classNames[ i ];
 
 					// Check each className given, space separated list
 					if ( self.hasClass( className ) ) {

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 );