vf-recaptcha-2.js

window.addEventListener("message", function(event) {

    if (event.data.type === 'CAPTCHA-SITEKEY') {
        sitekey = event.data.key;
        hostURL = event.data.hostURL;

        var gCaptchaScript = document.getElementById('g-captcha-script')

        if (!gCaptchaScript) {
            var script = document.createElement('script');
            head = document.head || document.getElementsByTagName('head')[0];
            script.src = `https://www.google.com/recaptcha/api.js?onload=onloadCallback&render=explicit`
            script.id = 'g-captcha-script'
            document.head.insertBefore(script, head.firstChild);
        }
    }