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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):
 """Wait for the Kindle Cloud Reader JS modules to initialize. These modules provide the interface used to execute API queries. """

    # Wait for the Module Manager to load
    mod_mgr_script = ur"return window.hasOwnProperty('KindleModuleManager');"
    mod_mgr_loaded = lambda br: br.execute_script(mod_mgr_script)
    self._wait(5).until(mod_mgr_loaded)

    # Wait for the DB Client to load
    db_client_script = dedent(ur"""
        var done = arguments[0];
        if (!window.hasOwnProperty('KindleModuleManager') ||
            !KindleModuleManager
                .isModuleInitialized(Kindle.MODULE.DB_CLIENT)) {
           done(false);
        } else {
            KindleModuleManager
                .getModuleSync(Kindle.MODULE.DB_CLIENT)
                .getAppDb()
                .getAllBooks()
                .done(function(books) { done(!!books.length); });
        }
        """)
    db_client_loaded = lambda br: br.execute_async_script(db_client_script)
    self._wait(5).until(db_client_loaded)