var xmlHttp 

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

function verificaUser(username){
xmlHttp=GetXmlHttpObject() 
if (xmlHttp==null){ 
alert ("Browserul tau nu suporta JavaScript.") 
return 
} 

var url="check.php?username="+username 
xmlHttp.open("GET",url,true) 
xmlHttp.onreadystatechange = function () { 
if (xmlHttp.readyState == 4) { 
document.getElementById("i1").className = xmlHttp.responseText; 
} 
}; 
xmlHttp.send(null); 
}