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>