function changeClassName( el, oldClass, newClass ){
    if ( el.className.match( new RegExp( '(\\s|^)'+oldClass+'(\\s|$)' ) ) ) {
        var reg = new RegExp( '(\\s|^)'+oldClass+'(\\s|$)' );
        el.className = el.className.replace( reg, ' ' );
    }
    if ( !el.className.match( new RegExp( '(\\s|^)'+newClass+'(\\s|$)' ) ) ) {
        el.className += ' '+newClass;
    }
}