[php] How to Validate Google reCaptcha on Form Submit

From a UX perspective, it can help to visibly let the user know when they can proceed to submit the form - either by enabling a disabled button, or simply making the button visible.

Here's a simple example...

<form>
    <div class="g-recaptcha" data-sitekey="YOUR_PRIVATE_KEY" data-callback="recaptchaCallback"></div>
    <button type="submit" class="btn btn-default hidden" id="btnSubmit">Submit</button>
</form>

<script>
    function recaptchaCallback() {
        var btnSubmit = document.getElementById("btnSubmit");

        if ( btnSubmit.classList.contains("hidden") ) {
            btnSubmit.classList.remove("hidden");
            btnSubmitclassList.add("show");
        }
    }
</script>

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