example/html/v3/index.html

<html>

<head>
    <title>reCAPTCHA demo: Simple page</title>
</head>

<body>
    <h3>
        <a href="https://developers.google.com/recaptcha/docs/v3">
            reCAPTCHA v3
        </a>
    </h3>
    <form action="/signin" method="POST">
        <input type="submit" value="Submit">
    </form>
    <div id="result"></div>
    <script src="https://www.google.com/recaptcha/api.js?render=your_site_key"></script>
    <script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"
        integrity="sha256-FgpCb/KJQlLNfOu91ta32o/NMZxltwRo8QtmkMRdAu8=" crossorigin="anonymous"></script>
    <script>
        var fetchToken = () => new Promise((resolve, reject) =>{
            grecaptcha.ready(function () {
                grecaptcha.execute('your_site_key', {
                     action: 'homepage' 
                }).then(function (token) {
                    console.log("g-recaptcha-response", token);
                    resolve(token);
                });
            });
        });
        var send = ()=>{
            fetchToken().then(token=>{
                let data = {
                    "other": "post data ...",
                    "token": token,
                };
                let jsonData = JSON.stringify(data);
                let url = "/signin";
                $.ajax({
                    method: "POST",
                    url: url,
                    data: jsonData
                }).done(function (msg) {
                    $("#result").html(msg.message)
                });
            });
        }
        $(function () {
            $("form").submit(function (event) {
                event.preventDefault(); 
                $("#result").html("loading")
                send();
            })
        });
    </script>
</body>

</html>