Untitled

How do I select and open a random link of a certain class on an external webpage?
var linksInCategory = document.$('.CategoryTreeLabel').href);
var randomLinkArray = Array(linksInCategory);

function goThere(link) {
    var the_url = randomLinkArray[Math.floor(Math.random()*randomLinkArray.length)];

    var new_window = window.open(the_url,"new_window","menubar, resizeable. location, toolbar, status, scrollbars");
}

</script>
    </head>
    <body>
        <form name="the_form">
            <input type="button" name="randomSportsArticle" class="broadGroups" onClick="goThere(this)" src="http://en.wikipedia.org/wiki/Category:Sports" value="Sports"></input>

        </form>
    </body>
<html>