$("#bankAccountNumber").change(function(){
alert("1");
var account = $("channelForm.bankAccount.account").val();
alert("2");
var reg = /^\d{19}$/g; // 以19位數字開頭，以19位數字結尾
if( !reg.test(account) )
{
alert("格式錯誤，應該是19位數字！");
}
})
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "https://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="https://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312" />
<title>驗證銀行賬號</title>
<style type="text/css">
<!–
.STYLE1 {color: #FF0000}
–>
</style>
<script language="javascript" type="text/javascript">
function check()
{
var account = document.form1.account.value;
var reg = /^\d{19}$/g; // 以19位數字開頭，以19位數字結尾
if( !reg.test(account) )
{
alert("格式錯誤，應該是19位數字！");
}
else
{
alert("驗證成功！");
}
}
</script>
</head>
<body>
<form id="form1" name="form1" method="post" action="">
<p>賬號：
<input type="text" name="account" id="account" />
<span class="STYLE1">* （19位數字）</span></p>
<p>
<input type="button" name="button" id="button" value="驗證" onclick="check()" />
</p>
</form>
</body>
</html>