纯文字版返回顶端的js代码

代码如下:
<script language="javascript">
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>
<a href="javascript:void(0)" onclick="goto_top()">【返回顶部】</a>