关于js 中邮件验证问题

<script type="text/javascript">
    function validate_email(field, alerttxt) {
        with (field) {
            apos = value.indexOf("@")
            dotpos = value.lastIndexOf(".")
            if (apos < 1 || dotpos - apos < 2)
            { alert(alerttxt); return false }
            else { return true }
        }
    }

    function validate_form(thisform) {
        with (thisform) {
            if (validate_email(email, "Not a valid e-mail address!") == false)
            { email.focus(); return false }
        }
    }
</script>

 

<form action=""onsubmit="return validate_form(this);" method="post">
Email: <input type="text" name="email" size="30">
<input type="submit" value="Submit">
</form>