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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 angularFrontendAppDir(self) -> str: """ Angular Frontend Dir This directory will be linked into the angular app when it is compiled. :return: The absolute path of the Angular2 app directory. """

        relDir = self._packageCfg.config.plugin.title(require_string)
        dir = os.path.join(self._pluginRoot, relDir)
        if not os.path.isdir(dir): raise NotADirectoryError(dir)
        return dir