var http;
    
	http = createRequestObject();
			
	function requestUsername( username ){
		var urlAddress = "request_username.php?username=" + username ;
        //alert( urlAddress );

		http.open('get', urlAddress); 
        http.onreadystatechange = handleUsername;
	    http.send(null);
	}
 
	function handleUsername(){
    
		if (http.readyState == 4 && http.status == 200){ 		
			var response = http.responseText;
            
            //alert( response );
            if( response == "EXIST" ){
                document.all.status_username.value = "";
                document.all.status_image.style.display = '';
                document.all.status_image.src = "img/x.png";
            }else if( response == "OK" ){
                document.all.status_username.value = "OK";
                document.all.status_image.style.display = '';
                document.all.status_image.src = "img/check.png";
            }
        }  
	}