document.addEventListener("DOMContentLoaded", function(event) { 

  $(function(){
    var shrinkHeader = 80;
    $(window).scroll(function() {
      var scroll = getCurrentScroll();
      if ( scroll >= shrinkHeader ) {
       $('body').addClass('shrink');
      }
      else {
       $('body').removeClass('shrink');
      }
      });
    function getCurrentScroll() {
      return window.pageYOffset || document.documentElement.scrollTop;
    }
  });
  
});