返回顶部

// 返回顶部模块制作
    var goBack = document.querySelector('.goBack');
    var nav = document.querySelector('nav');
    window.addEventListener('scroll', function() {
        if (window.pageYOffset >= nav.offsetTop) {
            goBack.style.display = 'block';
        } else {
            goBack.style.display = 'none';
        }
    });
    goBack.addEventListener('click', function() {
        window.scroll(0, 0);
    })