Insert Google reCAPTCHA into Marketo form with validation

recaptchaMarketo.js

/* Load the Google reCAPTCHA API : Make sure it loads somewhere above the insert code-->
<script src="https://www.google.com/recaptcha/api.js" async defer></script>
*/

/* Main code that inserts the reCAPTCHA into the marketo form */  
// Wait for Marketo form to load  
MktoForms2.whenReady(function (form) {                               
  // Insert the recap div after the last form row
  $( '<div id="recap"></div>' ).insertAfter( ".mktoFormRow:last-of-type" ); 
  // render the recap : replace with your site key
  grecaptcha.render('recap', {
    'sitekey' : 'INSERT_YOUR_SITE_KEY',
  });
  // Validate form based on Recap
  document.getElementById("mktFrmSubmit").onclick = function(){
    var v = grecaptcha.getResponse();
    if(v.length == 0) {
      event.preventDefault();
      form.submittable(false);
      // You can put some css error response here if you want
    }
    else {
      form.submittable(true);
    }
  };
});