Doesn't watch files continuously

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
	// ignored: /regexp/ - a regular expression for files or folders that should not be watched
	// ignored: (entry) => boolean - an arbitrary function which must return truthy to ignore an entry
	// For all cases expect the arbitrary function the path will have path separator normalized to '/'.
	// All subdirectories are ignored too
});

// Watchpack.prototype.watch({
//   files: Iterable<string>,
//   directories: Iterable<string>,
//   missing: Iterable<string>,
//   startTime?: number
// })
wp.watch({
	files: listOfFiles,
	directories: listOfDirectories,
	missing: listOfNotExistingItems,
	startTime: Date.now() - 10000
});
// starts watching these files and directories
// calling this again will override the files and directories
// files: can be files or directories, for files: content and existence changes are tracked
//        for directories: only existence and timestamp changes are tracked
// directories: only directories, directory content (and content of children, ...) and
//              existence changes are tracked.
//              assumed to exist, when directory is not found without further information a remove event is emitted
// missing: can be files or directorees,
//          only existence changes are tracked
//          expected to not exist, no remove event is emitted when not found initially
// files and directories are assumed to exist, when they are not found without further information a remove event is emitted
// missing is assumed to not exist and no remove event is emitted

wp.on("change", function(filePath, mtime, explanation) {
	// filePath: the changed file
	// mtime: last modified time for the changed file
	// explanation: textual information how this change was detected
});

wp.on("remove", function(filePath, explanation) {
	// filePath: the removed file or directory
	// explanation: textual information how this change was detected
});

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
// The watcher will keep aggregating events
// which can be received with getAggregated()

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

// Watchpack.prototype.getAggregated(): { changes: Set<string>, removals: Set<string> }
const { changes, removals } = wp.getAggregated();
// returns the current aggregated info and removes that from the watcher
// The next aggregated event won't include that info and will only emitted
// when futher changes happen
// Can also be used when paused.

// Watchpack.prototype.collectTimeInfoEntries(fileInfoEntries: Map<string, Entry>, directoryInfoEntries: Map<string, Entry>)
wp.collectTimeInfoEntries(fileInfoEntries, directoryInfoEntries);
// collects time info objects for all known 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

// Watchpack.prototype.getTimeInfoEntries()
var fileTimes = wp.getTimeInfoEntries();
// returns a Map with all known time info objects for files and directories
// similar to collectTimeInfoEntries but returns a single map with all entries

// (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

	this.watcher.on("add", this.onFileAdded.bind(this));
	this.watcher.on("addDir", this.onDirectoryAdded.bind(this));
	this.watcher.on("change", this.onChange.bind(this));
	this.watcher.on("unlink", this.onFileUnlinked.bind(this));
	this.watcher.on("unlinkDir", this.onDirectoryUnlinked.bind(this));
	this.watcher.on("error", this.onWatcherError.bind(this));

	if(data) {
	var ts = data[0] === data[1] ? data[0] + FS_ACCURENCY : data[0];
	if(ts > startTime)
	watcher.emit("change", data[1] + FS_ACCURENCY);

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