How to write code, already solved question?

Question

reCAPTCHA

Hello.
I have exactly the same problem as here - https://stackoverflow.com/questions/31687803/recap...
But for some reason, even with the answers, I can't solve it.
Here is the code:

<form id='demo-form' action="?" method="POST">
      <div class="g-recaptcha" data-callback="imNotARobot" data-sitekey="*********"></div>
<script type="text/javascript">
var imNotARobot = function() {
        console.info("Button was clicked");
};
</script>
</form>