window.addEventListener('scroll',()=>{
        let t = document.documentElement.scrollTop || document.body.scrollTop,
        nav = document.getElementsByClassName('nav')[0];
        t >= nav.offsetTop ? (nav.classList.add('fixed')) : (nav.classList.remove('fixed'));
})

Hello everyone, the above code cannot remove the class name add normally. . . Even if I reverse the order of add and remove, I still can't execute it;
I have been searching for this problem for a long time but cannot solve it, so I would like to ask for your advice. Thank you thank you.