document.getElementById('form1').onsubmit = function(){ return check_data(); };
function check_data()
{
var flag = true;
var message = ''; // 錯誤訊息
// 檢查收件者 (不能為空白)
var receiver = document.getElementById('receiver');
if( receiver.value == '' )
{
flag = false;
message += '收件者不能為空白\n';
}