js实现几秒后页面自动跳转

<script type="text/javascript">
    var num = 5;
    function countDown() {
        if (num >= 0) {
            var str = '';
            str += '系统将在 ' + num + ' 秒钟后自动返回 <a href="http://">首页<\/a>';
            document.getElementById('autoDir').innerHTML = str;
            num--;
            setTimeout(countDown, 1000);
        }
        else {
            window.location.href = "${cms.AppPath}/HealthIndex.aspx";        
        }
    }
    window.onload = countDown;
</script>

<div id="autoDir"></div>

支持 IE和火狐，已测试