JavaScript split() join() Idiom

// From @codepo8
// http://www.smashingmagazine.com/2010/04/20/seven-javascript-things-i-wish-i-knew-much-earlier-in-my-career/

// Take the list of class attributes on an element and add new class.
function addclass(elm,newclass){
  var classes = elm.className.split(' ');
  classes.push(newclass);
  elm.className = classes.join(' ');
}