watchpack

What is watchpack?

The watchpack npm package is a wrapper around the file-watching functionality of Node.js and chokidar. It provides a higher-level API for watching file changes in a specified directory or set of directories. It is often used in build tools and development servers to watch for file changes and trigger rebuilds or reloads.

What are watchpack's main functionalities?

Watching Files and Directories

This feature allows you to watch for changes in specific files and directories. You can listen for 'change' events on individual files and 'aggregated' events for batch changes.

const Watchpack = require('watchpack');

const wp = new Watchpack({
  // options
});

wp.watch({
  files: ['file1.js', 'file2.js'],
  directories: ['dir1', 'dir2'],
  missing: ['file3.js', 'file4.js']
});

wp.on('change', (filePath, mtime, explanation) => {
  console.log(`${filePath} changed`, mtime, explanation);
});

wp.on('aggregated', (changes, removals) => {
  console.log('Changes:', changes);
  console.log('Removals:', removals);
});

Pausing and Resuming Watch

This feature allows you to temporarily pause the watching process and resume it later. This can be useful when performing batch operations that should not trigger watch events.

const wp = new Watchpack({});

// Start watching
wp.watch({ files: ['file1.js'] });

// Pause watching
wp.pause();

// After some time, resume watching
wp.watch({ files: ['file1.js'] });

Getting Watched Items

This feature allows you to retrieve a list of all files that are currently being watched. This can be useful for debugging or logging purposes.

const wp = new Watchpack({});

wp.watch({ files: ['file1.js'] });

const watchedFiles = wp.getWatchedFiles();
console.log(watchedFiles); // Outputs: ['file1.js']

Other packages similar to watchpack

chokidar

Chokidar is a more low-level file watching library that watchpack uses under the hood. It provides more granular control over file watching and events but requires more setup and configuration compared to watchpack.

gaze

Gaze is another file watching library that offers similar functionality to watchpack. It allows you to watch files and directories for changes and supports patterns for file matching. It differs in its API and the way it handles events and patterns.

nodemon

Nodemon is a tool that helps develop node.js based applications by automatically restarting the node application when file changes in the directory are detected. While it also watches files for changes, its primary use case is different as it focuses on restarting applications rather than providing an API for developers to hook into file changes.

README

watchpack

Wrapper library for directory and file watching.

Concept

watchpack high level API doesn't map directly to watchers. Instead a three level architecture ensures that for each directory only a single watcher exists.

• The high level API requests DirectoryWatchers from a WatcherManager, which ensures that only a single DirectoryWatcher per directory is created.
• A user-faced Watcher can be obtained from a DirectoryWatcher and provides a filtered view on the DirectoryWatcher.
• Reference-counting is used on the DirectoryWatcher and Watcher to decide when to close them.
• The real watchers are created by the DirectoryWatcher.
• Files are never watched directly. This should keep the watcher count low.
• Watching can be started in the past. This way watching can start after file reading.
• Symlinks are not followed, instead the symlink is watched.

API

var Watchpack = require("watchpack");

var wp = new Watchpack({
	// options:
	aggregateTimeout: 1000,
	// fire "aggregated" event when after a change for 1000ms no additional change occurred
	// aggregated defaults to undefined, which doesn't fire an "aggregated" event

	poll: true,
	// poll: true - use polling with the default interval
	// poll: 10000 - use polling with an interval of 10s
	// poll defaults to undefined, which prefer native watching methods
	// Note: enable polling when watching on a network path
	// When WATCHPACK_POLLING environment variable is set it will override this option

	followSymlinks: true,
	// true: follows symlinks and watches symlinks and real files
	//   (This makes sense when symlinks has not been resolved yet, comes with a performance hit)
	// false (default): watches only specified item they may be real files or symlinks
	//   (This makes sense when symlinks has already been resolved)

	ignored: "**/.git"
	// ignored: "string" - a glob pattern for files or folders that should not be watched
	// ignored: ["string", "string"] - multiple glob patterns that should be ignored
	// All subdirectories are ignored too
});

// Watchpack.prototype.watch(files: Iterable<string>, directories: Iterable<string>, startTime?: number)
wp.watch(listOfFiles, listOfDirectories, Date.now() - 10000);
// starts watching these files and directories
// calling this again will override the files and directories

wp.on("change", function(filePath, mtime) {
	// filePath: the changed file
	// mtime: last modified time for the changed file (null if file was removed)
	// for folders it's a time before that all changes in the directory happened
});

wp.on("aggregated", function(changes, removals) {
	// changes: a Set of all changed files
	// removals: a Set of all removed files
	// watchpack gives up ownership on these Sets.
});

// Watchpack.prototype.pause()
wp.pause();
// stops emitting events, but keeps watchers open
// next "watch" call can reuse the watchers

// Watchpack.prototype.close()
wp.close();
// stops emitting events and closes all watchers

// Watchpack.prototype.getTimeInfoEntries()
var fileTimes = wp.getTimeInfoEntries();
// returns a Map with all known time info objects for files and directories
// this include info from files not directly watched
// key: absolute path, value: object with { safeTime, timestamp }
// safeTime: a point in time at which it is safe to say all changes happened before that
// timestamp: only for files, the mtime timestamp of the file

// (deprecated)
// Watchpack.prototype.getTimes()
var fileTimes = wp.getTimes();
// returns an object with all known change times for files
// this include timestamps from files not directly watched
// key: absolute path, value: timestamp as number