chokidar

What is chokidar?

The chokidar npm package is a file watching library that provides an efficient way to watch files and directories for changes. It is built on top of Node.js's native 'fs' module and uses native file system events where possible, but can also fall back to polling if necessary. It is designed to be cross-platform and works on macOS, Windows, and Linux.

What are chokidar's main functionalities?

File Watching

This feature allows you to watch files and directories for changes. The 'add' event is emitted when a file is added to the watched directory, 'change' when a file is changed, and 'unlink' when a file is removed.

const chokidar = require('chokidar');

const watcher = chokidar.watch('/path/to/dir', {ignored: /(^|[\/\\])\../});

watcher.on('add', path => console.log(`File ${path} has been added`));
watcher.on('change', path => console.log(`File ${path} has been changed`));
watcher.on('unlink', path => console.log(`File ${path} has been removed`));

Directory Watching

const chokidar = require('chokidar');

const watcher = chokidar.watch('/path/to/dir', {ignored: /^\

0

README

Chokidar

A neat wrapper around node.js fs.watch / fs.watchFile / fsevents.

See what's new in v1.0

Why?

Node.js fs.watch:

• Doesn't report filenames on OS X.
• Doesn't report events at all when using editors like Sublime on OS X.
• Often reports events twice.
• Emits most changes as rename.
• Has a lot of other issues
• Does not provide an easy way to recursively watch file trees.

Node.js fs.watchFile:

• Almost as bad at event handling.
• Also does not provide any recursive watching.
• Results in high CPU utilization.

Other node.js watching libraries:

• Are not using ultra-fast non-polling fsevents watcher implementation on OS X

Chokidar resolves these problems.

It is used in brunch, karma, PM2, socketstream, derby, watchify, and many others. It has proven itself in production environments.

Getting started

Install chokidar via node.js package manager:

npm install chokidar

Then just require the package in your code:

var chokidar = require('chokidar');

// One-liner for current directory, ignores .dotfiles
chokidar.watch('.', {ignored: /[\/\\]\./}).on('all', function(event, path) {
  console.log(event, path);
});



var watcher = chokidar.watch('file, dir, or glob', {
  ignored: /[\/\\]\./,
  persistent: true
});

var log = console.log.bind(console);

watcher
  .on('add', function(path) { log('File', path, 'has been added'); })
  .on('change', function(path) { log('File', path, 'has been changed'); })
  .on('unlink', function(path) { log('File', path, 'has been removed'); })
  // More events.
  .on('addDir', function(path) { log('Directory', path, 'has been added'); })
  .on('unlinkDir', function(path) { log('Directory', path, 'has been removed'); })
  .on('error', function(error) { log('Error happened', error); })
  .on('ready', function() { log('Initial scan complete. Ready for changes.'); })
  .on('raw', function(event, path, details) { log('Raw event info:', event, path, details); })

// 'add', 'addDir' and 'change' events also receive stat() results as second
// argument when available: http://nodejs.org/api/fs.html#fs_class_fs_stats
watcher.on('change', function(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*']);

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

// Only needed if watching is `persistent: true`.
watcher.close();

// Full list of options. See below for descriptions.
chokidar.watch('file', {
  persistent: true,

  ignored: '*.txt',
  ignoreInitial: false,
  followSymlinks: true,
  cwd: '.',

  usePolling: true,
  alwaysStat: false,
  depth: undefined,
  interval: 100,

  ignorePermissionErrors: false,
  atomic: true
});

API

chokidar.watch(paths, options) — takes one or more paths (which may be paths to files, dirs to be watched recursively, or glob patterns) and options:

Persistence

• 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.

Path filtering

• 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). Indicates whether chokidar should ignore the initial add events or not.
• 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 OS X overrides the useFsEvents default.
• useFsEvents (default: true on OS X). 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 OS X, 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.
• Polling-specific settings (effective when usePolling: true)
  • interval (default: 100). Interval of file system polling.
  • binaryInterval (default: 300). Interval of file system polling for binary files. (see list of binary extensions)

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.

Methods & Events

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.
• .unwatch(path / paths): Stop watching files, directories, or glob patterns. Takes an array of strings or just one string.
• .close(): Removes all listeners from watched files.

Install Troubleshooting

• npm WARN optional dep failed, continuing fsevents@n.n.n

  • This message is normal part of how npm handles optional dependencies and is not indicative of a problem. Even if accompanied by other related error messages, Chokidar should function properly.

• ERR! stack Error: Python executable "python" is v3.4.1, which is not supported by gyp.

  • You should be able to resolve this by installing python 2.7 and running: npm config set python python2.7

• gyp ERR! stack Error: not found: make

  • On Mac, install the XCode command-line tools

License

The MIT license.

Copyright (c) 2012 - 2015 Paul Miller (http://paulmillr.com) & Elan Shanker

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.