Function watchFile

lib/fs.js:3106–3145

* Watches for changes on `filename`. * @param {string | Buffer | URL} filename * @param {{ * bigint?: boolean; * persistent?: boolean; * interval?: number; * }} [options] * @param {( * current?: Stats, * previous?: Stats * ) => any} listener * @returns {watchers.StatWatcher}

(filename, options, listener)

 * @returns {watchers.StatWatcher}
 */
function watchFile(filename, options, listener) {
  const h = vfsState.handlers;
  if (h !== null) {
    const result = h.watchFile(filename, options, listener);
    if (result !== undefined) return result;
  }
  filename = getValidatedPath(filename);
  filename = pathModule.resolve(filename);
  let stat;

  if (options === null || typeof options !== 'object') {
    listener = options;
    options = null;
  }

  options = {
    // Poll interval in milliseconds. 5007 is what libev used to use. It's
    // a little on the slow side but let's stick with it for now to keep
    // behavioral changes to a minimum.
    interval: 5007,
    persistent: true,
    ...options,
  };

  validateFunction(listener, 'listener');

  stat = statWatchers.get(filename);
  const watchers = require('internal/fs/watchers');
  if (stat === undefined) {
    stat = new watchers.StatWatcher(options.bigint);
    stat[watchers.kFSStatWatcherStart](filename,
                                       options.persistent, options.interval);
    statWatchers.set(filename, stat);
  } else {
    stat[watchers.kFSStatWatcherAddOrCleanRef]('add');
  }

  stat.addListener('change', listener);
  return stat;
}

/**
 * Stops watching for changes on `filename`.