AJAX提交，无重定向

I'm trying to have some data send to submit.php. The data does submit but it redirects me to the submit.php page. How can I submit this with out changing page?

JS

function submitq() {
if (window.XMLHttpRequest) {
  xmlhttp=new XMLHttpRequest();
  }
else
  {
  xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
  }
xmlhttp.onreadystatechange=function()
  {
  if (xmlhttp.readyState==4 && xmlhttp.status==200)
    {
    document.getElementById("submitdata").value=xmlhttp.responseText;
    }
  }
xmlhttp.open("POST",submit.php,true);
xmlhttp.send();
}

Just figured it out.

The form can't have an action of a method because that will redirect it after it is posted.