mozilla-release/testing/web-platform/tests/webstorage/event_local_oldvalue.html

<!DOCTYPE HTML>
<html>
 <head>
  <title>WebStorage Test: localStorage event - oldValue</title>
  <script src="/resources/testharness.js"></script>
  <script src="/resources/testharnessreport.js"></script>
 </head>
 <body>
    <h1>event_local_oldValue</h1>
    <div id="log"></div>
    <script>
        async_test(function(t) {
            localStorage.clear();
            t.add_cleanup(function() { localStorage.clear() });

            self.fail = t.step_func(function(msg) {
                assert_unreached(msg);
                t.done();
            });

            var expected = [null, 'user1', null]
            function onStorageEvent(event) {
                assert_equals(event.oldValue, expected.shift());
                if (!expected.length) {
                    t.done();
                }
            }

            window.addEventListener('storage', t.step_func(onStorageEvent), false);

            var el = document.createElement("iframe");
            el.setAttribute('id', 'ifrm');
            el.setAttribute('src', 'resources/local_change_item_iframe.html');
            document.body.appendChild(el);
        }, "oldValue property test of local event - Local event is fired due to an invocation of the setItem(), clear() methods.");
    </script>
 </body>
</html>