Selenium Async JS execution idea?

gistfile1.py

class BaseTestCase(TestCase):
  def __init__(self, *args, **kwargs):
    super(BaseTestCase, self).__init__(*args, **kwargs)
    self._script_id = 0
  
  def my_sync_test(self):
    result = self.js("""
      var result = {foo: [1,2,3]};
      testDone(result);
    """)
    print result['foo']

  def my_async_test(self):
    result = self.js("""
      var start = (new Date()).getTime();
      setTimeout(function() {
        testDone([start, new Date().getTime()]);
      }, 1000);
    """)
    print result

  def js(script):
    self._script_id += 1;
    self.execute_script("""
      (function() {
        function testDone(result) {
          document.body.setAttribute("data-jsTest-%(id)d", JSON.stringify(result));
        }

        %(script)s
      })();
    """ % {'id': self._script_id, 'script': script}
    result = self.find_soon('body[data-jsTest-%d]' % self._script_id).attributes['data-jsTest-%d' % self._script_id]
    return json.loads(result)

win.