例子：10秒后同意按钮可点击

<body>


<div>
    <span id="daojishi">10</span>
    <input disabled="disabled" type="button" value="注册" id="anniu" />
</div>


</body>

<script type="text/javascript">
    
    
    window.setTimeout("daojishi()",1000);
    
    //功能：倒计时减1
    function daojishi()
    {
        //找到span
        var s = document.getElementById("daojishi");
        
        //判断
        if(parseInt(s.innerHTML)<=0)
        {
            document.getElementById("anniu").removeAttribute("disabled");
        }
        else
        {
        //获取内容，减1之后再交给span
        s.innerHTML = parseInt(s.innerHTML)-1;
        
        //每隔一秒调一次该方法
        window.setTimeout("daojishi()",1000);
        }        
    }
    
</script>