How can I make reCAPTCHA a required field?

I'm using Google reCAPTCHA and have been able to add the CAPTCHA component to my page inside a form. But when I submit the form there's no validation taking place to check if the CAPTCHA has been solved.

How do I validate that the CAPTCHA component has been solved when submitting my form? Or, in other words, how do I make my CAPTCHA component required?

if you want to use the native html5 popups, than here is the solution

JavaScript:

window.onload = function() {
    var $recaptcha = document.querySelector('#g-recaptcha-response');

    if($recaptcha) {
    	$recaptcha.setAttribute("required", "required");
    }
};

CSS:

#g-recaptcha-response {
    display: block !important;
    position: absolute;
    margin: -78px 0 0 0 !important;
    width: 302px !important;
    height: 76px !important;
    z-index: -999999;
    opacity: 0;
}

I had the same problem as yours and solved it this way:

First declare a variable that stores 1 or 0 depending or whether the user filled the capcha correctly.

var allowSubmit = false;

Then you need a function which gets executed when the user fills the reCapcha correctly:

function capcha_filled () {
    allowSubmit = true;
}

... and a function that gets executed when the reCapcha session expires:

function capcha_expired () {
    allowSubmit = false;
}

To tell reCapcha about your functions (callbacks), set those data-attributes in your html:

<div class="g-recaptcha"
   data-callback="capcha_filled"
   data-expired-callback="capcha_expired"
   data-sitekey="your site key"></div>

Or if you use explicit load:

  var onloadCallback = function() {
    grecaptcha.render('your_div_id', {
      'sitekey' : 'your_site_key',
      'callback': capcha_filled,
      'expired-callback': capcha_expired,
    });
  };

You need also a callback for the form submission:

function check_if_capcha_is_filled (e) {
    if(allowSubmit) return true;
    e.preventDefault();
    alert('Fill in the capcha!');
}

Finally add in the form the onsubmit attribute:

<form action="..." onsubmit="check_if_capcha_is_filled">

---

Note: as mentioned in the comments, a server validation is still needed. The code prevents accidentally submitting the form unless the capcha is filled and is only for user's convenience.

I found this to be a quick & easy way to do it. Add this to your headers:

<script>
window.onload = function() {
  var recaptcha = document.forms["myForm"]["g-recaptcha-response"];
  recaptcha.required = true;
  recaptcha.oninvalid = function(e) {
    // do something
    alert("Please complete the captcha");
  }
}
</script>

This only works in HTML5, and is (or should be) supported by these browsers: http://caniuse.com/#feat=form-validation

(The JS console in Chrome shows this error message: https://stackoverflow.com/questions/7168645/invalid-form-control-only-in-google-chrome , and I haven't been able to work around this. Hopefully someone else will improve this response.)

I checked for existance of #g-recaptcha-response:

function checkRecaptcha() {
    res = $('#g-recaptcha-response').val();

    if (res == "" || res == undefined || res.length == 0)
        return false;
    else
        return true;
}

//...

$('#frm-signup').submit(function(e) {

	if(!checkRecaptcha()) {
		$( "#frm-result" ).text("Please validate your reCAPTCHA.");
		return false;
	}
    //...
});
    

This really should be part of the docs...

Not sure if you already solved this, but you could use an addon to validate the Google recaptcha: http://formvalidation.io/addons/recaptcha2/

If you want a more friendly and descriptive message, you can add a required checkbox. This will ensure the html5 popup shows something like: "Please check this box if you want to proceed"

<div class="captcha">
   <div class="g-recaptcha" data-sitekey="Your Site Key" data-callback="removeFakeCaptcha"></div>
   <input type="checkbox" class="captcha-fake-field" tabindex="-1" required>
</div>

Add the code to remove the fake captcha once completed

window.removeFakeCaptcha = function() {
   document.querySelector('.captcha-fake-field').remove();
}

Then on the css you hide the checkbox and position it to the captcha box:

.captcha {
  position: relative;
}
.captcha-fake-field {
  background: transparent;
  bottom: 0;
  border: none;
  display: block;
  height: 1px;
  left: 12px;
  width: 1px;
  position: absolute;
  z-index: -1;
}

Working solution in 2022

Personally, I was not able to get any of the above solutions to work with my captcha. So I figured I would share my current working solution for those facing the same issue.

The accepted answer doesn't have a validation technique for when the captcha expires, the below solution addresses that.

My notes in the .js should explain the solution thoroughly.

JavaScript

// By default do not allow form submission.
var allow_submit = false

function captcha_filled () {
	/*
	 * This is called when Google get's the recaptcha response and approves it.
	 * Setting allow_submit = true will let the form POST as normal.
	 * */

	allow_submit = true
}

function captcha_expired () {
	/*
	 * This is called when Google determines too much time has passed and expires the approval.
	 * Setting allow_submit = false will prevent the form from being submitted.
	 * */

	allow_submit = false
}


function check_captcha_filled (e) {
    console.log('captcha-verified')
	/*
	 * This will be called when the form is submitted.
	 * If Google determines the captcha is OK, it will have
	 * called captcha_filled which sets allow_submit = true
	 * If the captcha has not been filled out, allow_submit
	 * will still be false.
	 * We check allow_submit and prevent the form from being submitted
	 * if the value of allow_submit is false.
	 * */

	// If captcha_filled has not been called, allow_submit will be false.
	// In this case, we want to prevent the form from being submitted.
	if (!allow_submit) {
		// This call prevents the form submission.
		// e.preventDefault()

		// This alert is temporary - you should replace it with whatever you want
		// to do if the captcha has not been filled out.
		alert('ERROR: Please verify you are human by filling out the captcha')

		return false
	}
    captcha_expired()
	return true
}

HTML

<form action="post" onsubmit="return check_captcha_filled()">
<!-- form items -->
<div class="g-recaptcha"
   data-callback="captcha_filled"
   data-expired-callback="captcha_expired"
   data-sitekey="your site key">
</div>
</form>

I find this very helpful:

<div class="g-recaptcha myPopover" data-sitekey="Your Key" 
        data-callback="recaptchaCallback">

You add a function to data-callback="recaptchaCallback" with this code:

var recaptchachecked=false; 
function recaptchaCallback() {
    recaptchachecked = true;
}

and a function were you return the value to use it in a other html-tag like this:

<form method="post" onsubmit="return isreCaptchaChecked()">
function isreCaptchaChecked()
{
    return recaptchachecked;
}

I hope this helps you.