callbacks.js

var sitekey = null;        
var hostUrl = null;

var onloadCallback = function () {
  grecaptcha.render('widget1', {
    'sitekey': sitekey,
    'callback': grecaptchaRenderCallback
  });
};

function grecaptchaRenderCallback(res) {
    parent.postMessage({
        action: "checkCAPTCHAState",
        isValid: res ? true : false
    }, '*');
}