var oBack = document.getElementById("back"); //回到顶部的按钮
window.onscroll = function(){
if (getScrollTop() >= 500) {
oBack.style.display = "block";
}else{
oBack.style.display = "none";
}
}
//点击回到顶部
var timer;
var flags = true;
oBack.onclick = function(){
if (flags == true) {
flags = false;
}else{
return;
}
var t = 0;
var b = getScrollTop();
var c = -b;
var d = 50;
timer = setInterval(function(){
t++;
var temp = Tween.Cubic.easeIn(t,b,c,d); //依赖于T尾恩JS,地址http://www.createjs.cc/tweenjs/
if (t==d) {
clearInterval(timer);
flags = true;
}
document.body.scrollTop = document.documentElement.scrollTop = temp;
},15);
}
//获取滚动条高度
function getScrollTop(){
return document.body.scrollTop || document.documentElement.scrollTop;
}