<script type="text/javascript">
    alert(AJS.Meta.get("user-display-name"));
    alert(AJS.Meta.get("remote-user"));
    alert(AJS.Meta.get("issue-key"));
</script>

Getting all values:

 <script type="text/javascript">
    var metas = document.getElementsByTagName('meta');
    for (var i = 0; i < metas.length; i++) { // loop through all the meta tags
        var metaName = metas[i].name; // grab all the meta tag's name attributes
        document.write(metas[i].name + ": " + metas[i].content + "<br>");
        };
</script>

See the values from Confluence here