klass

// Minimalist class (className) manipulation library
var klass = {
  has: function(elem, name) {
    return (' '+elem.className+' ').indexOf(' '+name+' ') != -1;
  },
  add: function(elem, name) {
    if(!klass.has(elem, name)) {
      elem.className += ' '+name;
    }
  },
  remove: function(elem, name) {
    elem.className = (' '+elem.className+' ').split(' '+name+' ').join(' ').slice(1, -1);
  },
  toggle: function(elem, name) {
    klass[klass.has(elem, name)? 'remove' : 'add'](elem, name);
  }
}

more triming, more caching, smaller size once closure-compiled.