Method watch

packages/angular_devkit/core/node/host.ts:230–266

(
    path: Path,
    _options?: virtualFs.HostWatchOptions,
  )

  // Some hosts may not support watching.
  watch(
    path: Path,
    _options?: virtualFs.HostWatchOptions,
  ): Observable<virtualFs.HostWatchEvent> | null {
    return new Observable<virtualFs.HostWatchEvent>((obs) => {
      loadFSWatcher();
      const watcher = new FSWatcher({ persistent: false });
      watcher.add(getSystemPath(path));

      watcher
        .on('change', (path) => {
          obs.next({
            path: normalize(path),
            time: new Date(),
            type: virtualFs.HostWatchEventType.Changed,
          });
        })
        .on('add', (path) => {
          obs.next({
            path: normalize(path),
            time: new Date(),
            type: virtualFs.HostWatchEventType.Created,
          });
        })
        .on('unlink', (path) => {
          obs.next({
            path: normalize(path),
            time: new Date(),
            type: virtualFs.HostWatchEventType.Deleted,
          });
        });

      return () => {
        void watcher.close();
      };
    }).pipe(publish(), refCount());
  }
}