if ($('#back-to-top').length) {
    var scrollTrigger = 100, // px
    backToTop = function () {
        var scrollTop = $(window).scrollTop();
        if (scrollTop > scrollTrigger) {
            $('#back-to-top').addClass('show');
        } else {
            $('#back-to-top').removeClass('show');
        }
    };
    backToTop();
    $(window).on('scroll', function () {
        backToTop();
    });
    $('#back-to-top').on('click', function (e) {
        e.preventDefault();
        $('html,body').animate({
            scrollTop: 0
        }, 700);
    });
}