var xmlHttp

function GetXmlHttpObject(){ 
var objXMLHttp=null 
if (window.XMLHttpRequest){ 
objXMLHttp=new XMLHttpRequest() 
}else if (window.ActiveXObject){ 
objXMLHttp=new ActiveXObject("Microsoft.XMLHTTP") 
} // End ElseIf.
return objXMLHttp 
} // Close Function

function CheckUsername(username){ 
xmlHttp=GetXmlHttpObject() 
if (xmlHttp==null){ 
alert ("Browser does not support HTTP Request") // Alert Them!
return // Returns.
} // End If.

var url="includes/username_check.php?username="+username 
xmlHttp.open("GET",url,true) 
xmlHttp.onreadystatechange = function () { 
if (xmlHttp.readyState == 4) { 
document.getElementById("usernameresult").innerHTML = xmlHttp.responseText;
} // End If.
}; // Close Function
xmlHttp.send(null); // Sends NULL instead of sending data.
} // Close Function.