How can I validate google reCAPTCHA v2 using javascript/jQuery?

Question

This Client side verification of reCaptcha - the following worked for me :

if reCaptcha is not validated on client side grecaptcha.getResponse(); returns null, else is returns a value other than null.

Javascript Code:

var response = grecaptcha.getResponse();

if(response.length == 0)
    //reCaptcha not verified

else
    //reCaptch verified

Use this to validate google captcha with simple javascript.

This code at the html body:

<div class="g-recaptcha" id="rcaptcha" style="margin-left: 90px;" data-sitekey="my_key"></div>
<span id="captcha" style="margin-left:100px;color:red" />

This code put at head section on call get_action(this) method form button:

function get_action(form) 
{
    var v = grecaptcha.getResponse();
    if(v.length == 0)
    {
        document.getElementById('captcha').innerHTML="You can't leave Captcha Code empty";
        return false;
    }
    else
    {
        document.getElementById('captcha').innerHTML="Captcha completed";
        return true; 
    }
}

If you render the Recaptcha on a callback

<script src="https://www.google.com/recaptcha/api.js?onload=onloadCallback&render=explicit" async defer></script>

using an empty DIV as a placeholder

<div id='html_element'></div>

then you can specify an optional function call on a successful CAPTCHA response

var onloadCallback = function() {
    grecaptcha.render('html_element', {
      'sitekey' : 'your_site_key',
      'callback' : correctCaptcha
    });
  };

The recaptcha response will then be sent to the 'correctCaptcha' function.

var correctCaptcha = function(response) {
    alert(response);
};

All of this was from the Google API notes :

Google Recaptcha v2 API Notes

I'm a bit unsure why you would want to do this. Normally you would send the g-recaptcha-response field along with your Private key to safely validate server-side. Unless you wanted to disable the submit button until the recaptcha was sucessful or such - in which case the above should work.

Hope this helps.

Paul

Simplified Paul's answer:

Source:

<script src="https://www.google.com/recaptcha/api.js"></script>

HTML:

<div class="g-recaptcha" data-sitekey="YOUR_KEY" data-callback="correctCaptcha"></div>

JS:

var correctCaptcha = function(response) {
        alert(response);
    };

I used HarveyEV's solution but misread it and did it with jQuery validate instead of Bootstrap validator.

  <script src="http://ajax.aspnetcdn.com/ajax/jquery.validate/1.14.0/jquery.validate.min.js"></script>
  <script>
    $("#contactForm").validate({
      submitHandler: function (form) {
        var response = grecaptcha.getResponse();
        //recaptcha failed validation
        if (response.length == 0) {
          $('#recaptcha-error').show();
          return false;
        }
          //recaptcha passed validation
        else {
          $('#recaptcha-error').hide();
          return true;
        }
      }
    });
  </script>