scollingShowHideElement.js

$(function(){
 var shrinkHeader = 400;
  $(window).scroll(function() {
    var scroll = getCurrentScroll();
      if ( scroll == shrinkHeader ) {
           $('.flechita').fadeIn("slow");
        }
        else {
            $('.flechita').fadeOut("slow");
        }
  });
	function getCurrentScroll() {
    return window.pageYOffset || document.documentElement.scrollTop;
    }
});