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<!-- Vanilla JS -->
<script>
  var timeOut;
  function scrollToTop() {
  	if (document.body.scrollTop!==0 || document.documentElement.scrollTop!==0){
  		window.scrollBy(0,-50);
  		timeOut=setTimeout('scrollToTop()',10);
  	}
  	else clearTimeout(timeOut);
}
</script>

<a href="#top" onclick="scrollToTop();return false">Back to Top &uarr;</a>

<!-- jQuery -->
$(".scroll-up").on("click", function(e) {
	e.preventDefault();
  $("html, body").animate({ scrollTop: 0 }, 600);
});

<a href="#" class="scroll-up">Back to Top &uarr;</a>