js定时执行Iframe页面刷新

<iframe id="armchatroom" width="100%" frameBorder="0" src="c.php" scrolling="no"></iframe>
<input type="button" onclick="javascript:chatIframeStop();" value="stop Refresh" />
<script type="text/javascript">
var chatIframeTimer = setInterval("chatIframeReload()",5000);//1000为1秒钟
function chatIframeReload()
{
document.getElementById('armchatroom').contentWindow.location.reload(true);
}
function chatIframeStop()
{
if(chatIframeTimer)
{
window.clearTimeout(chatIframeTimer);
}
}
</script>