Checks if an element has a given class
@private
@param {Element} el - element to search for the class
@param {String} className - class name to search for
function hasClass(el, className) {
    var test;

    if (el.classList) {
      test = el.classList.contains(className);
    } else {
      var className = new RegExp('(^| )' + className + '( |$)', 'gi');
      test = new RegExp(className).test(el.className);
    }

    return test;
  }