I am working on a jQuery tutorial... (yes ? switching from prototype to jQuery !) but I am stuck on a an error message I don't get the solution...  and muy script is very very simple

1. <script>
2. $(document).ready(function() {
3. var obj = jQuery.parseJSON('{"name":"John"}');
4. alert( obj.name === "John" );
5. });
6. </script>

I am using jquery-1.4.2.min.js ( loaded )

what's wrong with this code from the tutorial ?