页面顶放效果

页面顶置效果
<script>
//<![CDATA[
var goto_top_type = -1;
var goto_top_itv = 0;

function goto_top_timer()
{
var y = goto_top_type == 1 ? document.documentElement.scrollTop : document.body.scrollTop;
var moveby = 15;

y -= Math.ceil(y * moveby / 100);
if (y < 0) {
y = 0;
}

if (goto_top_type == 1) {
document.documentElement.scrollTop = y;
}
else {
document.body.scrollTop = y;
}

if (y == 0) {
clearInterval(goto_top_itv);
goto_top_itv = 0;
}
}

function goto_top()
{
if (goto_top_itv == 0) {
if (document.documentElement && document.documentElement.scrollTop) {
goto_top_type = 1;
}
else if (document.body && document.body.scrollTop) {
goto_top_type = 2;
}
else {
goto_top_type = 0;
}

if (goto_top_type > 0) {
goto_top_itv = setInterval('goto_top_timer()', 50);
}
}
}

//]]>
<script>

实例:
<a href="#" onclick="goto_top()">TOP</a>