function isEmailAddress(string) {
    return /^[^@]+@[^.]+(\.[^.]+)+$/.test(string);
}

function validate(form) {
    var controls = form.elements,
        emailAddress = controls['e-mail'].value;

    /* Validate other controls */

    if (!isEmailAddress(emailAddress)) {
        alert('Please enter a valid e-mail address.');
        return false;
    }
    if (emailAddress != controls['confirm_e-mail'].value) {
        alert('You may have mistyped your e-mail address.'
            + ' Please check both fields carefully and try again.');
        return false;
    }

    /* More validation */

    return true;
}