js收藏展开与隐藏，返回顶部

var a = document.getElementById("more");
var b = document.getElementById("moreList");
var c = document.getElementById("MOREall");
a.onclick = function(){
c.style.display="block";
b.style.display="block";
a.style.display="none";
};
// 动画效果
var timer = null;
b.onclick = function(){
cancelAnimationFrame(timer);
timer = requestAnimationFrame(function fn(){
var oTop = document.body.scrollTop || document.documentElement.scrollTop;
if(oTop > 0){
document.body.scrollTop = document.documentElement.scrollTop = oTop - 50;
timer = requestAnimationFrame(fn);
}else{
cancelAnimationFrame(timer);
}
});
};
// 直接回到顶部
// b.onclick = function () {
// var top = document.body.scrollTop || document.documentElement.scrollTop;
// scrollBy(0,-top)
// };