I am trying to override the getJSON function in jQuery to provide additional params and then call the original getJSON. I am fairly unfamiliar with JavaScript and have scraped this together from other similar examples. Most of the examples I have seen override the behavior from a function in the jQuery.fn namespace. Could someone help me by telling me what I am doing wrong?

<script type="text/javascript" src="./js/jquery-1.6.4.min.js"></script>
<script type="text/javascript">

    var _old = $.getJSON;
    $.getJSON = function(){
        alert("Calling overridden getJSON");    
        return _old.apply(this,arguments);

$(document).ready(function() {
    try {
        $(this).getJSON('ajax/test.json', function(data) {
            var items = [];
    catch (err)