function checksubmit()
{
	if(form1.full_name.value=='')
	{
		alert('Xin vui long nhap ten cua ban\n De chung toi co the lien he voi ban, cam on');
		form1.full_name.focus();
		return false;
	}
	if(form1.address.value=='')
	{
		alert('Xin vui long nhap dia chi cua ban, cam on');
		form1.address.focus();
		return false;
	}
	if(form1.phone.value=='')
	{
		alert('Xin vui long nhap so dien thoai\n De chung toi co the lien he voi ban, cam on');
		form1.phone.focus();
		return false;
	}
	if(form1.message.value=='')
	{
		alert('Xin vui long de lai loi nhan, cam on.');
		form1.message.focus();
		return false;
	}
	form1.submit();
	return true;
}

function trim(sString) 
{
	while (sString.substring(0,1) == ' ')
	{
	sString = sString.substring(1, sString.length);
	}
	while (sString.substring(sString.length-1, sString.length) == ' ')
	{
	sString = sString.substring(0,sString.length-1);
	}
	return sString;
}
function isemail(email) {
	var re = /^(\w|[^_]\.[^_]|[\-])+(([^_])(\@){1}([^_]))(([a-z]|[\d]|[_]|[\-])+|([^_]\.[^_])*)+\.[a-z]{2,3}$/i
	return re.test(email);
}

function checkblank(str)
{
	if (trim(str)=='')
		return true;
	else
		return false;
}	
function checkform(){
	if (checkblank(document.form1.full_name.value)) { alert('Xin vui long nhap ten cua ban\n De chung toi co the lien he voi ban, cam on');form1.full_name.focus(); return false;}
	if (!isemail(document.form1.email.value)) { alert('Xin vui long nhap dia chi email cua ban\n De chung toi co the lien he voi ban, cam on'); form1.email.focus();  return false;}
	if (checkblank(document.form1.phone.value)) { alert('Xin vui long nhap so dien thoai\n De chung toi co the lien he voi ban, cam on'); form1.phone.focus(); return false;}
	if (checkblank(document.form1.address.value)) { alert('Xin vui long nhap dia chi cua ban'); form1.address.focus(); return false;}
	if (checkblank(document.form1.message.value)) { alert('Xin vui long de lai loi nhan, cam on.'); form1.message.focus(); return false;}
	
	document.form1.submit();
}