var list = document.getElementsByClassName("list")[0]
window.onscroll = function(){
console.log(window.pageYOffset)
if(window.pageYOffset>500){
list.style.height = "0px"
}else{
list.style.height = "40px"
}
}
<div class="list">
</div>
.list{
width: 100%;
height: 40px;
background: red;
transform: 0.5s;
position: fixed;
top: 0;
}
body{
margin: 0;
padding: 0;
height: 3000px;
}