Minimal and efficient cross-platform file watching library
Node.js fs.watch:
rename.Node.js fs.watchFile:
Chokidar resolves these problems.
Initially made for Brunch (an ultra-swift web app build tool), it is now used in Microsoft’s Visual Studio Code, gulp, karma, PM2, browserify, webpack, BrowserSync, and many others. It has proven itself in production environments.
Version 3 is out! Check out our blog post about it: Chokidar 3: How to save 32TB of traffic every week
Chokidar does still rely 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.
On MacOS, chokidar by default uses a native extension exposing the Darwin
FSEvents API. This provides very efficient recursive watching compared with
implementations like kqueue available on most *nix platforms. Chokidar still
does have to do some work to normalize the events received that way as well.
On most other platforms, 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.
Install with npm:
npm install chokidar
Then require and use it in your code:
const chokidar = require('chokidar');
// One-liner for current directory
chokidar.watch('.').on('all', (event, path) => {
console.log(event, path);
});
// Example of a more typical implementation structure
// Initialize watcher.
const watcher = chokidar.watch('file, dir, glob, or array', {
ignored: /(^|[\/\\])\../, // ignore dotfiles
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', '**/other-file*']);
// Get list of actual paths being watched on the filesystem
var watchedPaths = watcher.getWatched();
// Un-watch some files.
await watcher.unwatch('new-file*');
// Stop watching.
// The method is async!
watcher.close().then(() => console.log('closed'));
// Full list of options. See below for descriptions.
// Do not use this example!
chokidar.watch('file', {
persistent: true,
ignored: '*.txt',
ignoreInitial: false,
followSymlinks: true,
cwd: '.',
disableGlobbing: false,
usePolling: false,
interval: 100,
binaryInterval: 300,
alwaysStat: false,
depth: 99,
awaitWriteFinish: {
stabilityThreshold: 2000,
pollInterval: 100
},
ignorePermissionErrors: false,
atomic: true // or a custom 'atomicity delay', in milliseconds (default 100)
});
chokidar.watch(paths, [options])
paths (string or array of strings). Paths to files, dirs to be watched
recursively, or glob patterns.
\),
because that’s how they work by the standard —
you’ll need to replace them with forward slashes (/).options (object) Options object as defined below:persistent (default: true). Indicates whether the process
should continue to run as long as files are being watched. If set to
false when using fsevents to watch, no more events will be emitted
after ready, even if the process continues to run.ignored (anymatch-compatible definition)
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.disableGlobbing (default: false). If set to true then the strings passed to .watch() and .add() are treated as
literal path names, even if they look like globs.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.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)useFsEvents (default: true on MacOS). Whether to use the
fsevents watching interface if available. When set to true explicitly
and fsevents is available this supercedes the usePolling setting. When
set to false on MacOS, usePolling: true becomes the default.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.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.chokidar.watch() produces an instance of FSWatcher. Methods of FSWatcher:
.add(path / paths): Add files, directories, or glob patterns 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, directories, or glob patterns.
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.If you need a CLI interface for your file watching, check out chokidar-cli, allowing you to execute a command on each change, or get a stdio stream of change events.
npm WARN optional dep failed, continuing fsevents@n.n.n
npm handles optional dependencies and is
not indicative of a problem. Even if accompanied by other related error messages,
Chokidar should function properly.TypeError: fsevents is not a constructor
rm -rf node_modules package-lock.json yarn.lock && npm install, or update your dependency that uses chokidar.ENOSP error on Linux, like this:
bash: cannot set terminal process group (-1): Inappropriate ioctl for device bash: no job control in this shell
Error: watch /home/ ENOSPCecho fs.inotify.max_user_watches=524288 | sudo tee -a /etc/sysctl.conf && sudo sysctl -pFor more detailed changelog, see full_changelog.md.
FSWatcher#close() method became async. That fixes IO race conditions related to close method.ignored option if needed. Improve initial Linux scan time by 50%.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).
MIT (c) Paul Miller (https://paulmillr.com), see LICENSE file.