当div在视口中时添加类(水平滚动)

window.addEventListener('scroll', function() {
  // 在这里编写代码
});

var divElement = document.getElementById('your-div-id'); // 替换为你的div元素的ID
var divRect = divElement.getBoundingClientRect();
var divLeft = divRect.left;
var divRight = divRect.right;

var viewportWidth = window.innerWidth || document.documentElement.clientWidth;

if (divLeft >= 0 && divRight <= viewportWidth) {
  // div元素在视口中
} else {
  // div元素不在视口中
}

if (divLeft >= 0 && divRight <= viewportWidth) {
  divElement.classList.add('your-class-name'); // 替换为你要添加的类名
}