if(jQuery(document).height() > jQuery(window).height()) {

	jQuery(".byg_scrolltop").addClass("scrolltop_show");

	jQuery(".scrolltop_top").css("display","none");

}



jQuery(window).scroll(function() {

	if(jQuery(window).scrollTop() < 500) {

		jQuery(".scrolltop_top").css("display","none");

	} else {

		jQuery(".scrolltop_top").removeAttr("style","");

	}

});



var new2_scroll_position = 0;

var last2_scroll_position;

window.addEventListener('scroll', function(e) {

  last2_scroll_position = window.scrollY;

 

  // 向下滚动

  if (new2_scroll_position < last2_scroll_position && last2_scroll_position > 2) {

    jQuery(".byg_scrolltop").removeClass("scrolltop_show");

 

  // 向上滚动

  } else if (new2_scroll_position > last2_scroll_position) {

    jQuery(".byg_scrolltop").addClass("scrolltop_show");

  }

 

  new2_scroll_position = last2_scroll_position;

}); 



function topFunction() {

	jQuery("html, body").animate({scrollTop: 0}, 500);

}