jquery.replaceClasses.js

// Removes all classes beginning with prefix, and replaces them
// with a prefix+suffix class. For example:
//     $('#blah').addClass('foobaz');
//     $('#blah').replaceClasses('foo', 'baz');
jQuery.fn.replaceClasses = function(prefix, suffix) {
    var re = new RegExp('^' + prefix);
    return this.each(function() {
        var classes = this.className.split(/\s+/);
        var newClasses = [];
        var i = classes.length;
        while (i--) {
            if (!re.test(classes[i])) {
                newClasses.push(classes[i]);
            }
        }
        newClasses.push(prefix + suffix);
        this.className = newClasses.join(' ');
    });
};