Manipulating classes with javascript. http://blog.alexanderdickson.com/manipulating-classes-with-javascript

script.js

// Back in the old days, classes were manipulated on elements simply with the className property. 
// This led to an awful lot of string manipulation for manipulating the class attribute.

Thankfully, the classList property has popped up recently.
var supportsClassList = ({}).toString.call(document.body.classList) == '[object DOMTokenList]';

the fallback implementation
var getClasses = function(element){
  return element.className.split(/\s+/);
}
var addClass = function(element, classname){
  return element.className += " " + className;
}
var removeClass = function(element, className){
  return element.className = (" " + element.className + " ").replace(" " + className + " ", " ");
}
var toggleClass = function(element, className){
  return ((" " + element.className + " ").indexOf(className) > -1 ? addClass : removeClass)(element, className);
}