How to use the jupyterlab.jupyterlab.jlpmapp.HERE function in jupyterlab

----------
    logger: :class:`~logger.Logger`, optional
        The logger instance.

    Returns
    -------
    A list of `WatchHelper` objects.
    """
    parent = pjoin(HERE, '..')

    if not osp.exists(pjoin(parent, 'node_modules')):
        yarn_proc = Process(['node', YARN_PATH], cwd=parent, logger=logger)
        yarn_proc.wait()

    logger = _ensure_logger(logger)
    ts_dir = osp.realpath(osp.join(HERE, '..', 'packages', 'metapackage'))

    # Run typescript watch and wait for the string indicating it is done.
    ts_regex = r'.* Found 0 errors\. Watching for file changes\.'
    ts_proc = WatchHelper(['node', YARN_PATH, 'run', 'watch'],
                          cwd=ts_dir, logger=logger, startup_regex=ts_regex)

    return [ts_proc]

def watch_packages(logger=None):
    """Run watch mode for the source packages.

    Parameters
    ----------
    logger: :class:`~logger.Logger`, optional
        The logger instance.

    Returns
    -------
    A list of `WatchHelper` objects.
    """
    parent = pjoin(HERE, '..')

    if not osp.exists(pjoin(parent, 'node_modules')):
        yarn_proc = Process(['node', YARN_PATH], cwd=parent, logger=logger)
        yarn_proc.wait()

    logger = _ensure_logger(logger)
    ts_dir = osp.realpath(osp.join(HERE, '..', 'packages', 'metapackage'))

    # Run typescript watch and wait for the string indicating it is done.
    ts_regex = r'.* Found 0 errors\. Watching for file changes\.'
    ts_proc = WatchHelper(['node', YARN_PATH, 'run', 'watch'],
                          cwd=ts_dir, logger=logger, startup_regex=ts_regex)

    return [ts_proc]

from urllib.request import Request, urlopen, urljoin, quote
from urllib.error import URLError

from jupyter_core.paths import jupyter_config_path
from jupyterlab_server.process import which, Process, WatchHelper
from notebook.nbextensions import GREEN_ENABLED, GREEN_OK, RED_DISABLED, RED_X

from .semver import Range, gte, lt, lte, gt, make_semver
from .jlpmapp import YARN_PATH, HERE


# The regex for expecting the webpack output.
WEBPACK_EXPECT = re.compile(r'.*/index.out.js')

# The dev mode directory.
DEV_DIR = osp.realpath(os.path.join(HERE, '..', 'dev_mode'))


def pjoin(*args):
    """Join paths to create a real path.
    """
    return osp.realpath(osp.join(*args))


def get_user_settings_dir():
    """Get the configured JupyterLab user settings directory.
    """
    settings_dir = os.environ.get('JUPYTERLAB_SETTINGS_DIR')
    settings_dir = settings_dir or pjoin(
        jupyter_config_path()[0], 'lab', 'user-settings'
    )
    return osp.realpath(settings_dir)

def _node_check(logger):
    """Check for the existence of nodejs with the correct version.
    """
    node = which('node')
    try:
        output = subprocess.check_output([node, 'node-version-check.js'], cwd=HERE)
        logger.info(output.decode('utf-8'))
    except Exception:
        data = _get_core_data()
        ver = data['engines']['node']
        msg = 'Please install nodejs %s before continuing. nodejs may be installed using conda or directly from the nodejs website.' % ver
        raise ValueError(msg)

try:
        logger.debug('Fetching URL: %s' % (req.full_url))
    except AttributeError:
        logger.debug('Fetching URL: %s' % (req.get_full_url()))
    try:
        with contextlib.closing(urlopen(req)) as response:
            return json.loads(response.read().decode('utf-8'))
    except URLError as exc:
        logger.warning(
            'Failed to fetch package metadata for %r: %r',
            name, exc)
        raise


if __name__ == '__main__':
    watch_dev(HERE)

def clean(app_dir=None, logger=None):
    """Clean the JupyterLab application directory."""
    logger = _ensure_logger(logger)
    app_dir = app_dir or get_app_dir()
    logger.info('Cleaning %s...', app_dir)
    if app_dir == pjoin(HERE, 'dev'):
        raise ValueError('Cannot clean the dev app')
    if app_dir == pjoin(HERE, 'core'):
        raise ValueError('Cannot clean the core app')
    for name in ['staging']:
        target = pjoin(app_dir, name)
        if osp.exists(target):
            _rmtree(target, logger)
    logger.info('Success!')

def _get_core_data():
    """Get the data for the app template.
    """
    with open(pjoin(HERE, 'staging', 'package.json')) as fid:
        return json.load(fid)

# Look for mismatched version.
        pkg_path = pjoin(staging, 'package.json')

        if osp.exists(pkg_path):
            with open(pkg_path) as fid:
                data = json.load(fid)
            if data['jupyterlab'].get('version', '') != version:
                _rmtree(staging, self.logger)
                os.makedirs(staging)

        for fname in ['index.js', 'webpack.config.js',
                      'webpack.prod.config.js',
                      '.yarnrc', 'yarn.js']:
            target = pjoin(staging, fname)
            shutil.copy(pjoin(HERE, 'staging', fname), target)

        # Remove an existing yarn.lock file
        # Because otherwise we can end up with unwanted duplicates
        # cf https://github.com/yarnpkg/yarn/issues/3967
        if osp.exists(pjoin(staging, 'yarn.lock')):
            os.remove(pjoin(staging, 'yarn.lock'))

        # Ensure a clean templates directory
        templates = pjoin(staging, 'templates')
        if osp.exists(templates):
            _rmtree(templates, self.logger)

        try:
            shutil.copytree(pjoin(HERE, 'staging', 'templates'), templates)
        except shutil.Error as error:
            # `copytree` throws an error if copying to + from NFS even though