why form is submitting without validating recaptcha

Cant get google recaptcha v2 to prevent form submission.

Step 1 

Put a js function in your form submit to validate the re-captcha:

<form action="/sign-visitors-log/" method="post" id="VisitorsLogForm" onsubmit="return validateRecaptcha();">

Step 2 : Then some js to stop the form submit if the user didn't tick the check box:

function validateRecaptcha() {
    var response = grecaptcha.getResponse();
    if (response.length === 0) {
        alert("not validated");
        return false;
    } else {
        alert("validated");
        return true;
    }
}