export default function onSourceChange()

in src/watcher.js [13:73]
45 lines of code
10 McCabe index (conditional complexity)

export default function onSourceChange({
  sourceDir,
  watchFile,
  watchIgnored,
  artifactsDir,
  onChange,
  shouldWatchFile,
  debounceTime = 500,
}) {
  // When running on Windows, transform the ignored paths and globs
  // as Watchpack does translate the changed files path internally
  // (See https://github.com/webpack/watchpack/blob/v2.1.1/lib/DirectoryWatcher.js#L99-L103).
  const ignored =
    watchIgnored && process.platform === 'win32'
      ? watchIgnored.map((it) => it.replace(/\\/g, '/'))
      : watchIgnored;

  // TODO: For network disks, we would need to add {poll: true}.
  const watcher = ignored ? new Watchpack({ ignored }) : new Watchpack();

  // Allow multiple files to be changed before reloading the extension
  const executeImmediately = false;
  onChange = debounce(onChange, debounceTime, executeImmediately);

  watcher.on('change', (filePath) => {
    proxyFileChanges({ artifactsDir, onChange, filePath, shouldWatchFile });
  });

  log.debug(
    `Watching ${watchFile ? watchFile.join(',') : sourceDir} for changes`,
  );

  const watchedDirs = [];
  const watchedFiles = [];

  if (watchFile) {
    for (const filePath of watchFile) {
      if (existsSync(filePath) && !lstatSync(filePath).isFile()) {
        throw new UsageError(
          'Invalid --watch-file value: ' + `"${filePath}" is not a file.`,
        );
      }

      watchedFiles.push(filePath);
    }
  } else {
    watchedDirs.push(sourceDir);
  }

  watcher.watch({
    files: watchedFiles,
    directories: watchedDirs,
    missing: [],
    startTime: Date.now(),
  });

  // TODO: support interrupting the watcher on Windows.
  // https://github.com/mozilla/web-ext/issues/225
  process.on('SIGINT', () => watcher.close());
  return watcher;
}