function backTop(btnId) { |
var btn = document.getElementById(btnId); |
var d = document.documentElement; |
var b = document.body; |
window.onscroll = set; |
btn.style.display = "none" ; |
btn.onclick = function () { |
btn.style.display = "none" ; |
window.onscroll = null ; |
this .timer = setInterval( function () { |
d.scrollTop -= Math.ceil((d.scrollTop + b.scrollTop) * 0.1); |
b.scrollTop -= Math.ceil((d.scrollTop + b.scrollTop) * 0.1); |
if ((d.scrollTop + b.scrollTop) == 0) clearInterval(btn.timer, window.onscroll = set); |
}, 10); |
}; |
function set() { |
btn.style.display = (d.scrollTop + b.scrollTop > 100) ? 'block' : "none" |
} |
}; |
backTop( 'goTop' ); |