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


Question

I have a simple contact form in aspx. I want to validate the reCaptcha (client-side) before submitting the form. Please help.

Sample code:

    <%@ Page Language="VB" AutoEventWireup="false" CodeFile="Default2.aspx.vb" Inherits="Default2" %>
    <!DOCTYPE html>
    <html xmlns="http://www.w3.org/1999/xhtml">
    <head runat="server">
        <title>Test Form</title>
        <link rel="stylesheet" href="//code.jquery.com/ui/1.11.2/themes/smoothness/jquery-ui.css">
        <script src="//code.jquery.com/jquery-1.10.2.js"></script>
        <script src="//code.jquery.com/ui/1.11.2/jquery-ui.js"></script>
        <link rel="stylesheet" href="/resources/demos/style.css">
        <script src="https://www.google.com/recaptcha/api.js" async defer></script>
        <script>
            $("#cmdSubmit").click(function () {
                //need to validate the captcha
            });
        </script> 
    </head>
    <body>
        <form id="form1" runat="server">
            <label class="clsLabe">First Name<sup>*</sup></label><br />
            <input type="text" id="txtFName" name="txtFName" class="clsInput" /><br />
            <div class="g-recaptcha" data-sitekey="my_key"></div>
            <img id="cmdSubmit" src="SubmitBtn.png" alt="Submit Form" style="cursor:pointer;" />
        </form>
    </body>
    </html>

I want to validate the captcha on cmdSubmit click.

Please help.

2015/01/12
1
122
1/12/2015 1:09:08 PM


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; 
    }
}
2016/07/29

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

2016/06/05

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);
    };
2016/03/09

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>
2016/02/15

I thought all of them were great but I had troubles actually getting them to work with javascript and c#. Here is what I did. Hope it helps someone else.

//put this at the top of the page
<script src="https://www.google.com/recaptcha/api.js"></script>

//put this under the script tag
<script>
var isCaptchaValid = false;
function doCaptchaValidate(source, args) {
    args.IsValid = isCaptchaValid;
}
var verifyCallback = function (response) {
    isCaptchaValid = true;
};
</script>

//retrieved from google and added callback
<div class="g-recaptcha" data-sitekey="sitekey" data-callback="verifyCallback">

//created a custom validator and added error message and ClientValidationFucntion
<asp:CustomValidator runat="server" ID="CustomValidator1" ValidationGroup="Initial" ErrorMessage="Captcha Required" ClientValidationFunction="doCaptchaValidate"/>
2017/02/15