Открыть всплывающее окно, когда я нажимаю на сторонний URL

$(document).on('click', 'a', function (e) {
    var a_id = $(this).attr('id');
    var href_val = $(this).attr('href');

    if (href_val[0] != '#' && href_val != undefined) {
        var j = href_val.indexOf("://");
        var host = "";
        for (i = j + 3; i < href_val.length; i++) {
            if (href_val.charAt(i) != '/') {
                host = host + "" + href_val.charAt(i);
            } else {
                break;
            }
        }
        var my_url = window.location.hostname;
        if (my_url != host) {
            if (a_id == undefined) {
                e.preventDefault();
                var href_val = $(this).attr('href');
                $('.popupHolder').show();
                $('.popupHolder h3 span').html(href_val);
            }
        }
    }
});
$("button.proceed").on('click', function (e) {
    window.location.href = $('.popupHolder h3 span').html();
});
$("button.cancel").on('click', function (e) {
    $('.popupHolder').hide();
});

.popupHolder {
    display: none;
    position: fixed;
    width: 100%;
    height: 100%;
    top: 0;
    left: 0;
    background-color: #fff;
    z-index: 999;
}

<script src = "https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<div class = "content">
    <h1 id = "back">Home</h1>
    <p>Lorem Ipsum is simply dummy text of the printing and typesetting industry. Lorem Ipsum has been the industry's
        standard
        dummy text ever since the 1500s, when an unknown printer took a galley of type and scrambled it to make a type
        specimen
        book. <a class = "external" href = "https://www.google.com/">Google.com</a> <a href = "#about">Hash Link About</a>
    </p>
</div>
<div class = "content">
    <h2 id = "about">About</h2>
    <p>Lorem Ipsum is simply dummy text of the <a class = "external" href = "https://www.facebook.com/">Facebook.com</a>
        printing and
        typesetting industry. Lorem Ipsum has been the industry's
        standard
        <a href = "#back">Back to Top</a>
    </p>
</div>
<div class = "content">
    <p><a href = "https://www.twitter.com/">Twitter.com</a>
        <a href = "#back">Back to Top</a>
    </p>
</div>
<div class = "popupHolder">
    <h3>Do you want to visit <span></span>?</h3>
    <button class = "proceed">Proceed</button>
    <button class = "cancel">Cancel</button>
</div>