Untitled

When using AJAX and php with Google Maps, page keeps refreshing
document.getElementById("msg").innerHTML=xmlhttp.responseText;

filename.html?searchterm=user+input+stuff

filename.html?searchterm=

<html>
<head>
<title>Map</title>
<link rel="stylesheet" type="text/css" href="stylue.css" />

<script type="text/javascript"
src="http://maps.googleapis.com/maps/api/js?
key=AIzaSyBksQ7NlV6eXk6w5w8222lolqdPHsN_8ls&sensor=false">
</script>

<script type="text/javascript">


var panorama;
var map;


function initialize() {

//create Google Map
}

//other Google Maps functions

function searchdb(userInput){

    var xmlhttp;
    if (userInput==""){
        document.getElementById("msg").innerHTML="No Text Entered";
    }else{
        if (window.XMLHttpRequest){
    xmlhttp=new XMLHttpRequest();
        }
  else{
    xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
        }


  xmlhttp.onreadystatechange=function(){
  if (xmlhttp.readyState==4 && xmlhttp.status==200){
    document.getElementById("msg").innerHTML=xmlhttp.responseText;
    alert(xmlhttp.responseText);
  }
        }
        xmlhttp.open("GET","searchpageajax.php?searchterm="+userInput,true);
        xmlhttp.send();
   }

}

window.onload= function () {
    initialize();
}


</script>


</head>
<body >

<h1>Map</h1>

<p>Enter a room code or building name to search.</p>

<form name="inputform" >
<input type="text" name="searchterm" />
<input type="submit" value="Search" onclick="searchdb(searchterm.value)"/>
<input type="reset" value="Clear" />
<br/>
<p id ="msg"></p>
<br/>
</form>


<div id="container">
    <div id="map_canvas"></div>
    <div id="streetview_canvas"></div>
</div>

</body>
</html>