// 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);
})