Javascript的interval绑定方法，每隔两秒执行该方法

<script type="text/javascript">
function interFunc( interval )
{
if(!interval)interval=2000;
var _timerID = window.setInterval("test();",interval);
}
function test()
{
alert("test function activated");
}
</script>

<button id = "btnTest" value="xxxx" onclick="javascript:interFunc();"></button>