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.

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');

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

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

// 'add', 'addDir' and 'change' events also receive stat() results as second argument.
// http://nodejs.org/api/fs.html#fs_class_fs_stats
watcher.on('change', function(path, stats) {
  console.log('File', path, 'changed size to', stats.size);
});

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

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

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

API

• chokidar.watch(paths, options): takes paths to be watched recursively and options:
  • options.ignored (regexp or function) files to be ignored. This function or regexp is tested against the whole path, not just filename. If it is a function with two arguments, 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).
  • options.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.
  • options.ignorePermissionErrors (default: false). Indicates whether to watch files that don't have read permissions.
  • options.ignoreInitial (default: false). Indicates whether chokidar should ignore the initial add events or not.
  • options.interval (default: 100). Interval of file system polling.
  • options.binaryInterval (default: 300). Interval of file system polling for binary files (see extensions in src/is-binary).
  • options.useFsEvents (default: true on OS X). Whether to use the fsevents watching interface if available. When set to true and fsevents is available this supercedes the usePolling setting.
  • options.usePolling (default: false on Windows, true on Linux and OS X). Whether to use fs.watchFile (backed by polling), or fs.watch. If polling leads to high CPU utilization, consider setting this to false. Polling may be necessary to successfully watch files in certain situation, such as network mounted drives.
  • options.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.
  • options.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.

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

• .add(file / files): Add directories / files for tracking. Takes an array of strings (file paths) or just one path.
• .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.
• .close(): Removes all listeners from watched files.

License

The MIT license.

Copyright (c) 2014 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.