Multiple reCAPTCHA

recaptcha.html

<script src="https://www.google.com/recaptcha/api.js?onload=onloadCallback&render=explicit" async defer></script>

<div class="form-group">
    <div class="g-recaptcha" id="optional-id"></div>
</div>

<script type="text/javascript" charset="utf-8">
    var onloadCallback = function() {
        var recaptchas = document.querySelectorAll('div[class=g-recaptcha]');

        for( i = 0; i < recaptchas.length; i++) {
            grecaptcha.render( recaptchas[i].id, {
            'sitekey' : '6Lc-google-reCAPTCHA-site-key',
            });
        }
    }
</script>