essentials.js

    Element.prototype.addClass = function (className) {
      if (this.className.indexOf(className) === -1)
        this.className = this.className + ' '+className;
    };

    Element.prototype.hasClass = function (className) {
      return (this.className.indexOf(className) > -1);
    }

    Element.prototype.removeClass = function (className) {
      this.className = this.className.replace(className, '');
    };