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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _wait_for_js(self):
 """ Class method added by the decorators to allow decorated classes to manually re-check JavaScript dependencies. Expect that `self` is a class that: 1) Has been decorated with either `js_defined` or `requirejs` 2) Has a `browser` property If either (1) or (2) is not satisfied, then do nothing. """


    # No Selenium browser available, so return without doing anything
    if not hasattr(self, 'browser'):
        return

    # pylint: disable=protected-access
    # Wait for JavaScript variables to be defined
    if hasattr(self, '_js_vars') and self._js_vars:
        EmptyPromise(
            lambda: _are_js_vars_defined(self.browser, self._js_vars),
            u"JavaScript variables defined: {0}".format(", ".join(self._js_vars))
        ).fulfill()

    # Wait for RequireJS dependencies to load
    if hasattr(self, '_requirejs_deps') and self._requirejs_deps:
        EmptyPromise(
            lambda: _are_requirejs_deps_loaded(self.browser, self._requirejs_deps),
            u"RequireJS dependencies loaded: {0}".format(", ".join(self._requirejs_deps)),
            try_limit=5
        ).fulfill()