function backToTop() {
    let toTopBtn = $(‘#toTopBtn‘);
    let scrollTop = $(document).scrollTop();
    let clientHeight = document.documentElement.clientHeight;
    toggleToTopBtn(toTopBtn, scrollTop, clientHeight);
    $(window).on(‘scroll‘, () => {
        scrollTop = $(document).scrollTop();
        toggleToTopBtn(toTopBtn, scrollTop, clientHeight);
    })
    toTopBtn.on(‘click‘, () => {
        $(‘body,html‘).animate({
            scrollTop: 0
        }, 500)
    })
}

function toggleToTopBtn(toTopBtn, scrollTop, clientHeight) {
    if (scrollTop > clientHeight) {
        toTopBtn.css(‘visibility‘, ‘visible‘);
    } else {
        toTopBtn.css(‘visibility‘, ‘hidden‘);
    }
}