To top JS and HTML

to-top.html

<!-- 1 -->
<a href="#" id="totop">TOP</a>
<script>
	if ($('#totop').length) {
        var scrollTrigger = 100, // px
            backToTop = function () {
                var scrollTop = $(window).scrollTop();
                if (scrollTop > scrollTrigger) {
                    $('#totop').addClass('show');
                } else {
                    $('#totop').removeClass('show');
                }
            };
        backToTop();
        $(window).on('scroll', function () {
            backToTop();
        });
        $('#totop').on('click', function (e) {
            e.preventDefault();
            $('html,body').animate({
                scrollTop: 0
            }, 700);
        });
    }
</script>


<!-- 2 -->
<div class="go2top">
	<i class="fa fa-chevron-up"></i>
</div>
<script>
	var LayoutGo2Top = function () {
        var handle = function () {
            var currentWindowPosition = $(window).scrollTop(); // current vertical position
            if (currentWindowPosition > 300) {
                $(".go2top").show();
            } else {
                $(".go2top").hide();
            }
        };

        return {
            //main function to initiate the module
            init: function () {
                handle(); // call headerFix() when the page was loaded
                if (navigator.userAgent.match(/iPhone|iPad|iPod/i)) {
                    $(window).bind("touchend touchcancel touchleave", function (e) {
                        handle();
                    });
                } else {
                    $(window).scroll(function () {
                        handle();
                    });
                }

                $(".go2top").on('click', function (e) {
                    e.preventDefault();
                    $("html, body").animate({
                        scrollTop: 0
                    }, 600);
                });
            }
        };
    }();
    LayoutGo2Top.init();
</script>

I personally adopt the second one in https://github.com/arturmamedov/withfront