Contact form with Google Scripts

contact.gs

var secret = '<recaptcha_secret>';
var tomail = '<mail>@gmail.com';

function doGet(e) {
    return ContentService.createTextOutput('Hayirdir?');
}

function doPost(e) {
    var captchakey = (e.parameters.captcha) || "";
    var name = (e.parameters.name) || "";
    var email = (e.parameters.email) || "";
    var message = (e.parameters.message) || "";
    var form_gonder = (e.parameters.formgonder) || "";
    var returnval = "ok";

    captchakey = captchakey.toString();
    name = name.toString();
    email = email.toString();
    message = message.toString();
    form_gonder = form_gonder.toString();


    if (form_gonder != "1" || isBlank(captchakey) || isBlank(name) || isBlank(email) || isBlank(message))
        returnval = "bos_alan_var";

    if (returnval == "ok")
        if (verifyCaptcha(captchakey)) {
            MailApp.sendEmail({
                to: tomail,
                subject: "gokay.biz iletisim!",
                replyTo: getTextFromHtml(email),
                htmlBody: "<h4 style='text-transform: capitalize; margin-bottom: 0'>İsim: </h4>" + "<div>" + getTextFromHtml(name) + "</div>" + "<h4 style='text-transform: capitalize; margin-bottom: 0'>Mail: </h4>" + "<div>" + getTextFromHtml(email) + "</div>" + "<h4 style='text-transform: capitalize; margin-bottom: 0'>Mesaj: </h4>" + "<div>" + getTextFromHtml(message) + "</div>"
            });
            returnval = "ok||" + name;
        } else
            returnval = "captcha";


    return ContentService.createTextOutput(returnval);
}

function isBlank(str) {
    return (!str || /^\s*$/.test(str));
}

function getTextFromHtml(html) {
    return getTextFromNode(Xml.parse(html, true).getElement());
}

function getTextFromNode(x) {
    switch (x.toString()) {
        case 'XmlText':
            return x.toXmlString();
        case 'XmlElement':
            return x.getNodes().map(getTextFromNode).join('');
        default:
            return '';
    }
}

function verifyCaptcha(gRecaptchaResponse) {
    var payload = {
        'secret': secret,
        'response': gRecaptchaResponse
    }
    var url = 'https://www.google.com/recaptcha/api/siteverify';
    var resp = UrlFetchApp.fetch(url, {
        payload: payload,
        method: 'POST'
    }).getContentText();
    return JSON.parse(resp).success;
}