Hugo Googly Analytics with cookie consent

extend_head.html

<div id="cookie-notice">
    <span>We would like to use third party cookies and scripts to improve the
        functionality of this website.</span>
    <a id="cookie-notice-accept" class="button">Accept</a>
    <a id="cookie-notice-deny" class="button">No Thanks</a>
    <a href="/privacy">More info</a>
</div>

<script>
    function createCookie(name, value, days) {
        var expires = "";
        if (days) {
            var date = new Date();
            date.setTime(date.getTime() + (days * 24 * 60 * 60 * 1000));
            expires = "; expires=" + date.toUTCString();
        }
        document.cookie = name + "=" + value + expires + "; path=/";
    }
    function cookieExists(name) {
        return document.cookie.split(';').some((item) => item.trim().startsWith(name)) ? true : false;
    }

    function readCookie(name) {
        if (cookieExists(name)) {
            return document.cookie.split('; ').find(row => row.startsWith(name)).split('=')[1];
        }
        return null;
    }
    
    function eraseCookie(name) {
        createCookie(name, "", -1);
    }

    if (readCookie('cookie-notice-option') == 'true') {
        {{ if hugo.IsProduction | or (eq .Site.Params.env "production") }}

        // Initialize Google Analytics
        {{ with .Site.GoogleAnalytics -}}
        {{ if hasPrefix . "G-"}}
            function loadScriptAsync(scriptSrc, callback) {
                if (typeof callback !== 'function') {
                    throw new Error('Not a valid callback for async script load');
                }
                var script = document.createElement('script');
                script.onload = callback;
                script.src = scriptSrc;
                document.head.appendChild(script);
            }

            /* This is the part where you call the above defined function and "calls back" 
            your code which gets executed after the script has loaded */
            loadScriptAsync('https://www.googletagmanager.com/gtag/js?id={{ . }}', function () {
                window.dataLayer = window.dataLayer || [];
                function gtag() { dataLayer.push(arguments); }
                gtag('js', new Date());
                gtag('config', '{{ . }}', { 'anonymize_ip': true });
            })
        {{- end -}}
        {{- end }}

        {{ end }}
    } else if (readCookie('cookie-notice-option') == null) {
        document.getElementById('cookie-notice').style.display = 'block';
    }

    document.getElementById('cookie-notice-accept').addEventListener("click", function () {
        createCookie('cookie-notice-option', 'true', 31);
        document.getElementById('cookie-notice').style.display = 'none';
        location.reload();
    });

    document.getElementById('cookie-notice-deny').addEventListener("click", function () {
        createCookie('cookie-notice-option', 'false', 31);
        document.getElementById('cookie-notice').style.display = 'none';
        location.reload();
    });

</script>