function gid (id)
{
    return document.getElementById(id);
}

function validMailAddress (mailAddress)
{
    var regExpMail = new RegExp("[A-Za-z0-9_]+([-+.][A-Za-z0-9_]+)*@[A-Za-z0-9_]+([-.][A-Za-z0-9_]+)*\\.[A-Za-z0-9_]{2,}([-.][A-Za-z0-9_]+)*");
    var result = regExpMail.exec(mailAddress);
    return (null == result) ? false : true;
}

function validation ()
{
    var errors = '';

    if (false == validMailAddress(gid('mail-input').value)) {
        errors += 'Please enter e-mail\n';
    }
    
    if ('' != errors) {
        alert(errors);
        return false;
    }
    return true;
}