$(document).ready(function(){

    $('.dropdown').width($('.mainButton').width()-2);

    $('.mainButton').hover(
      function () {
        $('.javascriptHook', this).addClass('slide-down'); 
        $('.dropdown', this).slideDown(100);
      }, 
      function () {
        obj = this;
        $('.dropdown', this).slideUp(100, function(){ $('.javascriptHook', obj).removeClass('slide-down'); });
      }
    );

});