vf-recaptcha-3.js

/*
 *  If a message was received not from the expected origin, let's bail.
 */
if (event.origin !== hostURL){
    return;
}

/*
 *  Let's check for a recaptcha token and send back the result to our component.
 */
if (event.data.action == "alohaCallingCAPTCHA"){
    var token = document.getElementById("g-recaptcha-response").value;

    if (token == ""){
        parent.postMessage({
            action: "alohaCallingCAPTCHA",
            alohaResponseCAPTCHA : "NOK"
        }, hostURL);
    }  else {
        parent.postMessage({
            action: "alohaCallingCAPTCHA",
            alohaResponseCAPTCHA : "OK",
            response: token
        },  hostURL);
    }
}
}, false);