Quick jQuery style add/remove class implementation.

addRemove.js

(function() {
  
  // Helper which turns class string into array
  function getClassList(element) {
    return element.getAttribute('class').split(' ');
  }

  // Add class with this name to the element
  function addClass(name) {
    var classes = getClassList(this);
    
    if(classes.indexOf(name) < 0) {
      classes.push(name);
    }

    this.setAttribute('class', classes.join(' '));
  }

  // Remove class with this name
  function removeClass(name) {
    var classes, index;

    classes = getClassList(this);
    
    if((index = classes.indexOf(name)) >= 0) {
      classes.splice(index, 1);
    }

    this.setAttribute('class', classes.join(' '));
  }

  Element.prototype.addClass = addClass;
  Element.prototype.removeClass = removeClass;
})();