prototype-classname-functions.js

var hasClassName = function(element, className) {
  var elementClassName = element.className;
  return (elementClassName.length > 0 && (elementClassName == className ||
    new RegExp("(^|\\s)" + className + "(\\s|$)").test(elementClassName)));
}
var addClassName = function(element, className) {
  if (!hasClassName(element, className))
  element.className += (element.className ? ' ' : '') + className;
  return element;
}
var removeClassName = function(element, className) {
  element.className = element.className.replace(
    new RegExp("(^|\\s+)" + className + "(\\s+|$)"), ' ').replace(/^\s+/, '').replace(/\s+$/, '');
  return element;
}