404.html

<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Call To</title>
    <link id="style" rel="stylesheet" href="/trigger-call-link/index.css">
</head>

<body class="p-8 text-center container mx-auto max-w-2xl">
    <div id="valid" class="block">
        <h1 class="uppercase text-gray-500">Number</h1>
        <a id="number" href="#" class="block text-3xl text-purple-800 font-bold my-4"></a>
        <a id="button" href="#" class="block text-2xl bg-purple-900 text-white py-5 font-bold my-10">Call Number</a>
    </div>
    <div id="invalid" class="hidden text-xl uppercase text-gray-500">
        No number has been provided in the URL.
    </div>
    <script>
        function numberOnly(string) {
            return string.replace(/[^\+\d]/ig, '');
        }

        function renderCall() {
            var query = window.location.search;
            var path = window.location.pathname;
            var number = numberOnly(query) || numberOnly(path) || null;

            if (!number) {
                document.getElementById('valid').classList.add('hidden');
                document.getElementById('valid').classList.remove('block');

                document.getElementById('invalid').classList.remove('hidden');
            } else {
                document.getElementById('number').innerText = number;
                document.getElementById('number').setAttribute('href', "tel:" + number)
                document.getElementById('button').setAttribute('href', "tel:" + number)
            }

            if ((query + path).indexOf('autocall') >= 0) {
                window.location.href = 'tel:' + number;
            }
        }

        renderCall();

        if (window.location.hostname.indexOf('localhost') >= 0) {
            document.getElementById('style').setAttribute('href', '/index.css');
        }
    </script>
</body>

</html>