js返回页面顶部

第一次写博客，不太专业，废话不多说，直接上自己早上做的东东。有不足之处，希望指点。

css:

body{counter-reset: p;}
p{width: 100px;margin: 20px 0;font: normal 40px/1.5 Arial;text-align: center;border: 1px solid #ccc;}
p:before{content: counter(p);counter-increment: p;}

.scrollTop,.scrollBottom{position: fixed;right: 30px;width: 40px;height: 40px;border: 2px solid #1FA879;border-radius: 5px;cursor: pointer;}
.scrollTop{bottom: 100px;}
.scrollBottom{bottom: 40px;}
.scrollTop:before,.scrollBottom:before{content: "";position: absolute;left: 9px;border: 11px solid transparent;}
.scrollTop:before{top: 3px;border-bottom-color: #1FA879;}
.scrollBottom:before{top: 15px;border-top-color: #1FA879;}
.scrollTop:hover,.scrollBottom:hover{background: #1FA879;}
.scrollTop:hover:before{border-bottom-color: #fff;}
.scrollBottom:hover:before{border-top-color: #fff;}

HTML:

<p></p><p></p><p></p><p></p><p></p><p></p><p></p><p></p><p></p><p></p><p></p><p></p><p></p><p></p><p></p><p></p><p></p><p></p><p></p><p></p><p></p><p></p><p></p><p></p><p></p><p></p><p></p><p></p><p></p><p></p><p></p><p></p><p></p><p></p><p></p><p></p><p></p><p></p><p></p><p></p>

<div class="scrollTop" id="scrollTop"></div>
<div class="scrollBottom" id="scrollBottom"></div>

JavaScript:

<script>
  (function () {
    var top=document.getElementById("scrollTop"),
        bottom=document.getElementById("scrollBottom"),
        timerTop,timerBottom,timerMove,delayScroll=13,delayMove=23,rate=0.95;

    top.onclick=function () {
      clear(timerTop,timerBottom);
      timerTop=setInterval(function() {
        if(setTop(getPos().st*rate)===0) clear(timerTop);
      }, delayScroll);
    };

    bottom.onclick=function () {
      clear(timerTop,timerBottom);
      timerBottom=setInterval(function() {
        var r=getPos(),_y=Math.ceil((r.sh-r.st-r.ch)*(1-rate));
        if(setTop(_y+r.st)===r.st) clear(timerBottom);
      }, delayScroll);
    };

    top.onmouseover=function () {
      clear(timerMove);
      timerMove=setInterval(function() {
        scrollBy(0,-1);
        if(getPos().st===0) clear(timerMove);
      }, delayMove);
    };

    bottom.onmouseover=function () {
      clear(timerMove);
      timerMove=setInterval(function() {
        scrollBy(0,1);
        var r=getPos();
        if(r.st===r.sh-r.ch) clear(timerMove);
      }, delayMove);
    };

    top.onmouseout=bottom.onmouseout=function () {
      clear(timerMove);
    }

    function getPos() {
      return {
        sh:document.documentElement.scrollHeight,
        ch:document.documentElement.clientHeight||document.body.clientHeight,
        st:window.scrollY||document.documentElement.scrollTop||document.body.scrollTop
      };
    }

    function setTop(s) {
      return document.documentElement.scrollTop=document.body.scrollTop=s;
    }

    function clear() {
      for (var i = 0; i < arguments.length; clearInterval(arguments[i]),i++);
    }
  })();
</script>

看DEMO戳我