recaptcha-v3

recaptcha-client.js

function initRecaptcha () {
    // If you want recaptcha enabled on a form, give it the data-recaptcha attribute
    var recaptchaForms = document.querySelectorAll('form[data-recaptcha]');

    recaptchaForms.forEach(form => {
        form.addEventListener('submit', e => {
            e.preventDefault();

            grecaptcha.ready(function() {
                grecaptcha.execute('PUBLICKEY', { action: 'submit' }).then(function(token) {
                    // Directly creates and appends hidden field with recaptcha response to the form
                    var input = document.createElement("input");
                    
                    input.setAttribute("type", "hidden");
                    input.setAttribute("name", "g-recaptcha-response");
                    input.setAttribute("value", token);
                    
                    form.appendChild(input);
                    form.submit();
                });
            });
        });
    });
}

initRecaptcha();

recaptcha-server.php

<?php
// This code goes in your form handler
$captcha = $_POST['g-recaptcha-response'];
$secret = 'SECRETKEY';
$querystring = '?secret=' . $secret . '&response=' . $captcha;

// This is a GET Request, replace `wp_remote_get` if not using wordpress
$recaptcha_response = wp_remote_get(
    'https://www.google.com/recaptcha/api/siteverify' . $querystring
);