function Ajax_signup(obj)
{
    
    var username    = document.getElementById('new_username').value;
    var password    = document.getElementById('new_password').value;   
    var email       = document.getElementById('new_email').value;
    var age         = document.getElementById('new_age').value;
    var sex;
    
    var reg = '^[\.a-zA-Z0-9_-]+$';
    
    if(!username.match(reg) || !password.match(reg) || username.length > 40 || password.length > 40 || username.length == 0 || password.length ==0) {
        alert('[Ten tai khoan] va [password] yeu cau 40 ki tu; 0-9  a-z  A-z  .  _  -'); 
        return false;
    }
    
    if(!parseInt(age)) {
        alert('Tuoi khong chap nhan');
        return false;
    }
    
    var reg = '^[\.a-zA-Z0-9_-]+\@[a-zA-Z0-9_-]+\.[\.a-zA-Z]+$';
    if(!email.match(reg)) {
        alert('Email khong chap nhan duoc');
        return false;
    }
	
	var _anti_spam = document.getElementById('anti_spam').value;
	if(_anti_spam.length != 7) {
		alert('Vui long nhap lai ma anti-spam !');
        return false;
	}
    
    
    // lay thong tin gioi tinh
    var getSex  = document.getElementsByName('sex');
    if(getSex[0].checked) sex = 0;
    else    sex = 1;
    
    
    obj.style.display   = 'none'; 
    
    // da co day du du kien load ajax
    var XMLhttp = getAjaxCore();
    
    XMLhttp.onreadystatechange  = function()
    {
        
        var inner       = document.getElementById('ajax_loading');
        
        var availWidth  = parseInt(document.documentElement.clientWidth)/2 - 300 + 'px';
        
        inner.style.left    = availWidth;
        inner.style.top     = 300 + 'px';
        
        inner.style.display = 'block';
        
        // scroll on top
            
        if(XMLhttp.readyState   != 4) {
            var img = '<center><img src="gui/ajax-loader3.gif"></center>'; 
            if(inner.innerHTML  != img) inner.innerHTML = img;   
        }
        
        // get data
        else {
            if(XMLhttp.responseText == 'true') {
                
                var content = '<center>Tai khoan da duoc tao. Ban co the dang nhap ngay bay gio</center>';
                inner.innerHTML  = content;    
                
            } else { 
                inner.innerHTML    = '<center><span style="color:red;">Co loi xay ra, vui long nhap lai thong tin dang ki.</span></center>'; 
            }
           
        }

       
    }
    
    
    // sending request
    var url = 'Ajax_script/signup.ajax.php?username={username}&password={password}&email={email}&age={age}&sex={sex}&anti_spam={anti_spam}&tmp={random}';
    url = url.replace('{username}', encodeURIComponent(username));
    url = url.replace('{password}', encodeURIComponent(password));
    url = url.replace('{email}', encodeURIComponent(email));
    url = url.replace('{age}', encodeURIComponent(age));
    url = url.replace('{sex}', encodeURIComponent(sex));
    url = url.replace('{random}', Math.random());
	url = url.replace('{anti_spam}', encodeURIComponent(_anti_spam));
    
    XMLhttp.open('GET', url, true);
    XMLhttp.send(null);
    
    return true;
    
}