请问这个js为什么不能实现倒计时

Question

 <a><script type="text/javascript">document.write(10)</script>秒钟后将返回首页</a>
                     <script type="text/javascript"> 
        function jump()
        {
            location.href="/visitors";
        }    
        var s=0;    
        function show()
        {
            s=s+1;
            if (s>10) return;
            o=document.getElementById('second');
            o.innerHTML=(10-s)+'秒钟后将会跳转到首页';
        }   
        setTimeout('jump()',10*1000);
        setInterval('show()',1000);
    </script>这段js可以自动跳转页面，但是页面不能显示倒计时...

Answer 1

 <a id="second"><script type="text/javascript">document.write(10)</script>秒钟后将返回首页</a>
                     <script type="text/javascript"> 
        function jump()
        {
            location.href="/visitors";
        }    
        var s=0;    
        function show()
        {
            s=s+1;
            if (s>10) return;
            o=document.getElementById('second');
            o.innerHTML=(10-s)+'秒钟后将会跳转到首页';
        }   
        setTimeout('jump()',10*1000);
        setInterval('show()',1000);
    </script>

Answer 2

<a id="second">10秒钟后将返回首页</a>
<script type="text/javascript">
    var a=document.getElementById("second");
    var i=10;
    setInterval(function(){
        i--;
        if(i<1){
            location.href="/visitors";
        }else{
            a.innerHTML=i+"秒钟后将返回首页";
        }
    },1000);
</script>