chokidar

Minimal and efficient cross-platform file watching library

paulmillr

11039

585

JavaScript

Chokidar

Minimal and efficient cross-platform file watching library

Why?

There are many reasons to prefer Chokidar to raw fs.watch / fs.watchFile in 2024:

Events are properly reported
- macOS events report filenames
- events are not reported twice
- changes are reported as add / change / unlink instead of useless rename
Atomic writes are supported, using atomic option
- Some file editors use them
Chunked writes are supported, using awaitWriteFinish option
- Large files are commonly written in chunks
File / dir filtering is supported
Symbolic links are supported
Recursive watching is always supported, instead of partial when using raw events
- Includes a way to limit recursion depth

Chokidar relies on the Node.js core fs module, but when using
fs.watch and fs.watchFile for watching, it normalizes the events it
receives, often checking for truth by getting file stats and/or dir contents.
The fs.watch-based implementation is the default, which
avoids polling and keeps CPU usage down. Be advised that chokidar will initiate
watchers recursively for everything within scope of the paths that have been
specified, so be judicious about not wasting system resources by watching much
more than needed. For some cases, fs.watchFile, which utilizes polling and uses more resources, is used.

Made for Brunch in 2012,
it is now used in ~30 million repositories and
has proven itself in production environments.

Sep 2024 update: v4 is out! It decreases dependency count from 13 to 1, removes
support for globs, adds support for ESM / Common.js modules, and bumps minimum node.js version from v8 to v14.
Check out upgrading.

Getting started

Install with npm:

npm install chokidar

Use it in your code:

import chokidar from 'chokidar';

// One-liner for current directory
chokidar.watch('.').on('all', (event, path) => {
  console.log(event, path);
});


// Extended options
// ----------------

// Initialize watcher.
const watcher = chokidar.watch('file, dir, or array', {
  ignored: (path, stats) => stats?.isFile() && !path.endsWith('.js'), // only watch js files
  persistent: true
});

// Something to use when events are received.
const log = console.log.bind(console);
// Add event listeners.
watcher
  .on('add', path => log(`File ${path} has been added`))
  .on('change', path => log(`File ${path} has been changed`))
  .on('unlink', path => log(`File ${path} has been removed`));

// More possible events.
watcher
  .on('addDir', path => log(`Directory ${path} has been added`))
  .on('unlinkDir', path => log(`Directory ${path} has been removed`))
  .on('error', error => log(`Watcher error: ${error}`))
  .on('ready', () => log('Initial scan complete. Ready for changes'))
  .on('raw', (event, path, details) => { // internal
    log('Raw event info:', event, path, details);
  });

// 'add', 'addDir' and 'change' events also receive stat() results as second
// argument when available: https://nodejs.org/api/fs.html#fs_class_fs_stats
watcher.on('change', (path, stats) => {
  if (stats) console.log(`File ${path} changed size to ${stats.size}`);
});

// Watch new files.
watcher.add('new-file');
watcher.add(['new-file-2', 'new-file-3']);

// Get list of actual paths being watched on the filesystem
let watchedPaths = watcher.getWatched();

// Un-watch some files.
await watcher.unwatch('new-file');

// Stop watching. The method is async!
await watcher.close().then(() => console.log('closed'));

// Full list of options. See below for descriptions.
// Do not use this example!
chokidar.watch('file', {
  persistent: true,

  // ignore .txt files
  ignored: (file) => file.endsWith('.txt'),
  // watch only .txt files
  // ignored: (file, _stats) => _stats?.isFile() && !file.endsWith('.txt'),

  awaitWriteFinish: true, // emit single event when chunked writes are completed
  atomic: true, // emit proper events when "atomic writes" (mv _tmp file) are used

  // The options also allow specifying custom intervals in ms
  // awaitWriteFinish: {
  //   stabilityThreshold: 2000,
  //   pollInterval: 100
  // },
  // atomic: 100,

  interval: 100,
  binaryInterval: 300,

  cwd: '.',
  depth: 99,

  followSymlinks: true,
  ignoreInitial: false,
  ignorePermissionErrors: false,
  usePolling: false,
  alwaysStat: false,
});

chokidar.watch(paths, [options])

paths (string or array of strings). Paths to files, dirs to be watched
recursively.
options (object) Options object as defined below:

Persistence

persistent (default: true). Indicates whether the process
should continue to run as long as files are being watched.

Path filtering

ignored function, regex, or path. Defines files/paths to be ignored.
The whole relative or absolute path is tested, not just filename. If a function with two arguments
is provided, it gets called twice per path - once with a single argument (the path), second
time with two arguments (the path and the
fs.Stats
object of that path).
ignoreInitial (default: false). If set to false then add/addDir events are also emitted for matching paths while
instantiating the watching as chokidar discovers these file paths (before the ready event).
followSymlinks (default: true). When false, only the
symlinks themselves will be watched for changes instead of following
the link references and bubbling events through the link’s path.
cwd (no default). The base directory from which watch paths are to be
derived. Paths emitted with events will be relative to this.

Performance

usePolling (default: false).
Whether to use fs.watchFile (backed by polling), or fs.watch. If polling
leads to high CPU utilization, consider setting this to false. It is
typically necessary to set this to true to successfully watch files over
a network, and it may be necessary to successfully watch files in other
non-standard situations. Setting to true explicitly on MacOS overrides the
useFsEvents default. You may also set the CHOKIDAR_USEPOLLING env variable
to true (1) or false (0) in order to override this option.
Polling-specific settings (effective when usePolling: true)
- interval (default: 100). Interval of file system polling, in milliseconds. You may also
  set the CHOKIDAR_INTERVAL env variable to override this option.
- binaryInterval (default: 300). Interval of file system
  polling for binary files.
  (see list of binary extensions)
alwaysStat (default: false). If relying upon the
fs.Stats
object that may get passed with add, addDir, and change events, set
this to true to ensure it is provided even in cases where it wasn’t
already available from the underlying watch events.
depth (default: undefined). If set, limits how many levels of
subdirectories will be traversed.
awaitWriteFinish (default: false).
By default, the add event will fire when a file first appears on disk, before
the entire file has been written. Furthermore, in some cases some change
events will be emitted while the file is being written. In some cases,
especially when watching for large files there will be a need to wait for the
write operation to finish before responding to a file creation or modification.
Setting awaitWriteFinish to true (or a truthy value) will poll file size,
holding its add and change events until the size does not change for a
configurable amount of time. The appropriate duration setting is heavily
dependent on the OS and hardware. For accurate detection this parameter should
be relatively high, making file watching much less responsive.
Use with caution.
- options.awaitWriteFinish can be set to an object in order to adjust
  timing params:
- awaitWriteFinish.stabilityThreshold (default: 2000). Amount of time in
  milliseconds for a file size to remain constant before emitting its event.
- awaitWriteFinish.pollInterval (default: 100). File size polling interval, in milliseconds.

Errors

ignorePermissionErrors (default: false). Indicates whether to watch files
that don’t have read permissions if possible. If watching fails due to EPERM
or EACCES with this set to true, the errors will be suppressed silently.
atomic (default: true if useFsEvents and usePolling are false).
Automatically filters out artifacts that occur when using editors that use
“atomic writes” instead of writing directly to the source file. If a file is
re-added within 100 ms of being deleted, Chokidar emits a change event
rather than unlink then add. If the default of 100 ms does not work well
for you, you can override it by setting atomic to a custom value, in
milliseconds.

Methods & Events

chokidar.watch() produces an instance of FSWatcher. Methods of FSWatcher:

.add(path / paths): Add files, directories for tracking.
Takes an array of strings or just one string.
.on(event, callback): Listen for an FS event.
Available events: add, addDir, change, unlink, unlinkDir, ready,
raw, error.
Additionally all is available which gets emitted with the underlying event
name and path for every event other than ready, raw, and error. raw is internal, use it carefully.
.unwatch(path / paths): Stop watching files or directories.
Takes an array of strings or just one string.
.close(): async Removes all listeners from watched files. Asynchronous, returns Promise. Use with await to ensure bugs don’t happen.
.getWatched(): Returns an object representing all the paths on the file
system being watched by this FSWatcher instance. The object’s keys are all the
directories (using absolute paths unless the cwd option was used), and the
values are arrays of the names of the items contained in each directory.

CLI

Check out third party chokidar-cli,
which allows to execute a command on each change, or get a stdio stream of change events.

Troubleshooting

Sometimes, Chokidar runs out of file handles, causing EMFILE and ENOSP errors:

bash: cannot set terminal process group (-1): Inappropriate ioctl for device bash: no job control in this shell
Error: watch /home/ ENOSPC

There are two things that can cause it.

Exhausted file handles for generic fs operations
- Can be solved by using graceful-fs,
  which can monkey-patch native fs module used by chokidar: let fs = require('fs'); let grfs = require('graceful-fs'); grfs.gracefulify(fs);
- Can also be solved by tuning OS: echo fs.inotify.max_user_watches=524288 | sudo tee -a /etc/sysctl.conf && sudo sysctl -p.
Exhausted file handles for fs.watch
- Can’t seem to be solved by graceful-fs or OS tuning
- It’s possible to start using usePolling: true, which will switch backend to resource-intensive fs.watchFile

All fsevents-related issues (WARN optional dep failed, fsevents is not a constructor) are solved by upgrading to v4+.

Changelog

v4 (Sep 2024): remove glob support and bundled fsevents. Decrease dependency count from 13 to 1. Rewrite in typescript. Bumps minimum node.js requirement to v14+
v3 (Apr 2019): massive CPU & RAM consumption improvements; reduces deps / package size by a factor of 17x and bumps Node.js requirement to v8.16+.
v2 (Dec 2017): globs are now posix-style-only. Tons of bugfixes.
v1 (Apr 2015): glob support, symlink support, tons of bugfixes. Node 0.8+ is supported
v0.1 (Apr 2012): Initial release, extracted from Brunch

Upgrading

If you’ve used globs before and want do replicate the functionality with v4:

// v3
chok.watch('**/*.js');
chok.watch("./directory/**/*");

// v4
chok.watch('.', {
  ignored: (path, stats) => stats?.isFile() && !path.endsWith('.js'), // only watch js files
});
chok.watch('./directory');

// other way
import { glob } from 'node:fs/promises';
const watcher = watch(await Array.fromAsync(glob('**/*.js')));

// unwatching
// v3
chok.unwatch('**/*.js');
// v4
chok.unwatch(await glob('**/*.js'));

Also

Why was chokidar named this way? What’s the meaning behind it?

Chowkidar is a transliteration of a Hindi word meaning ‘watchman, gatekeeper’, चौकीदार. This ultimately comes from Sanskrit _ चतुष्क_ (crossway, quadrangle, consisting-of-four). This word is also used in other languages like Urdu as (چوکیدار) which is widely used in Pakistan and India.