index.html

index.html

  // 1
        <script src="https://code.jquery.com/jquery-3.4.1.min.js" integrity="sha256-CSXorXvZcTkaix6Yvo6HppcZGetbYMGWSFlBw8HfCJo="
  crossorigin="anonymous"></script>

        // 2
        <script src="https://www.google.com/recaptcha/api.js?render=reCAPTCHA_site_key"></script>
        <script>
          // 3
          grecaptcha.ready(function() {
              // 4
              $('#contactform').submit(function(e){
                  var form = this;
                  // 5
                  e.preventDefault()
                  grecaptcha.execute('reCAPTCHA_site_key', {action: 'contactform'}).then(function(token) {
                      // 6
                      $('#recaptcha').val(token)
                      // 7
                      form.submit()
                  });
              })
          });
         </script>