Using Ajax in Javascript

sendMail.html

<script type="text/javascript">	
function sendMailMessage()
{
	document.getElementById("sendbutton").innerHTML="<img src='images/loading.gif' border='0'>";
	
    if (window.XMLHttpRequest)
    {// code for IE7+, Firefox, Chrome, Opera, Safari
    	xmlhttp=new XMLHttpRequest();
    }
    else
    {// code for IE6, IE5
    	xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
    }
	
	var name = document.getElementById('name').value;
	var email = document.getElementById('email').value;
	var msg = document.getElementById('msg').value;
	
	var queryString = "?name="+name+"&email="+email+"&msg="+msg;
	
	xmlhttp.open("GET","sendMailMessage.php" + queryString,true);
	xmlhttp.send();
	
	xmlhttp.onreadystatechange=function()
    {
		if (xmlhttp.readyState==4 && xmlhttp.status==200)
		{
		 	document.getElementById('sendbutton').innerHTML=xmlhttp.responseText;
		}
    }
}
</script>