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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 bokehjssrcdir(self):
        ''' The absolute path of the BokehJS source code in the installed
        Bokeh source tree.

        '''
        if self._is_dev or self.debugjs:
            bokehjssrcdir = abspath(join(ROOT_DIR, '..', 'bokehjs', 'src'))

            if isdir(bokehjssrcdir):
                return bokehjssrcdir

        return None