@push.rocks/smartwatch

A cross-runtime file watcher with glob pattern support for Node.js, Deno, and Bun.

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Install

npm install @push.rocks/smartwatch
# or
pnpm add @push.rocks/smartwatch

Features

• Cross-Runtime — Works on Node.js 20+, Deno, and Bun
• Glob Pattern Support — Watch files using patterns like **/*.ts and src/**/*.{js,jsx}
• RxJS Observables — Subscribe to file system events using reactive streams
• Dynamic Watching — Add or remove watch patterns at runtime
• Write Stabilization — Built-in debouncing and awaitWriteFinish support for atomic writes
• TypeScript First — Full TypeScript support with comprehensive type definitions

How It Works

smartwatch selects the best file watching backend for the current platform and runtime:

| Platform and runtime | Backend | |--------------------------------------|----------------------------------| | Linux x64/arm64, any runtime | Bundled Rust binary built on the notify crate (inotify), driven over IPC by @push.rocks/smartrust | | Node.js/Bun elsewhere | chokidar v5 (uses fs.watch() internally) | | Deno elsewhere | Native Deno.watchFs() API |

The package ships statically linked Rust binaries for Linux x64 and arm64 (glibc and musl), and smartwatch prefers them on Node.js, Deno and Bun alike. Without a binary for the platform, chokidar provides robust cross-platform file watching on Node.js and Bun with features like atomic write detection, inode tracking, and write stabilization, and on Deno the native APIs are used directly with built-in debouncing and temporary file filtering.

Glob patterns are handled through picomatch — base paths are extracted from patterns and watched natively, while events are filtered through matchers before emission. Relative patterns resolve against the working directory when start() runs, and a path without glob characters watches that file, or that directory and everything below it.

Usage

Basic Setup

import { Smartwatch } from '@push.rocks/smartwatch';

// Create a watcher with glob patterns
const watcher = new Smartwatch([
  './src/**/*.ts',
  './public/assets/**/*'
]);

// Start watching
await watcher.start();

start() resolves once the initial scan of the watched paths is complete. Files and directories that already exist at that point are the baseline and are not reported: subscribers receive add, addDir, change, unlink and unlinkDir only for changes made after start() resolved. This holds on every platform and runtime, and again for every start() that follows a stop().

A start() that cannot complete rejects and leaves the watcher idle, so it can be started again:

| Error | When | |--------------------------------|---------------------------------------------------------------| | SmartwatchStoppedError | stop() was called before start() completed | | SmartwatchStartTimeoutError | the initial scan did not complete within startTimeoutMs (default 30 seconds) | | SmartwatchScanError | the initial scan failed, for example with EMFILE (too many open files); cause holds the underlying error |

All three extend SmartwatchError and are exported from the package:

import { Smartwatch, SmartwatchStoppedError } from '@push.rocks/smartwatch';

try {
  await watcher.start();
} catch (error) {
  if (!(error instanceof SmartwatchStoppedError)) throw error;
  // stop() was called while starting: nothing to do
}

Subscribing to File Events

Use RxJS observables to react to file system changes. getObservableFor() resolves at once, before or after start():

// Get an observable for file changes
const changeObservable = await watcher.getObservableFor('change');
changeObservable.subscribe(([path, stats]) => {
  console.log(`File changed: ${path}`);
  console.log(`New size: ${stats?.size} bytes`);
});

// Watch for new files
const addObservable = await watcher.getObservableFor('add');
addObservable.subscribe(([path]) => {
  console.log(`File added: ${path}`);
});

// Watch for deleted files
const unlinkObservable = await watcher.getObservableFor('unlink');
unlinkObservable.subscribe(([path]) => {
  console.log(`File deleted: ${path}`);
});

Supported Events

| Event | Description | |-------------|--------------------------------| | add | File has been added | | addDir | Directory has been added | | change | File has been modified | | unlink | File has been removed | | unlinkDir | Directory has been removed | | error | Error occurred | | ready | Initial scan complete (emitted just before start() resolves; subscribe before start() to observe it) |

Dynamic Watch Management

Add or remove patterns while the watcher is running:

const watcher = new Smartwatch(['./src/**/*.ts']);
await watcher.start();

// Add more patterns to watch
watcher.add(['./tests/**/*.spec.ts', './config/*.json']);

// Remove a pattern
watcher.remove('./src/**/*.test.ts');

Stopping the Watcher

await watcher.stop();

stop() also cancels a start() that is still running: that start() rejects with SmartwatchStoppedError. stop() resolves once the watcher is released, and a later start() begins afresh.

Complete Example

import { Smartwatch } from '@push.rocks/smartwatch';

async function watchProject() {
  const watcher = new Smartwatch([
    './src/**/*.ts',
    './package.json'
  ]);

  await watcher.start();
  console.log('Watching for changes...');

  const changes = await watcher.getObservableFor('change');
  changes.subscribe(([path, stats]) => {
    console.log(`Modified: ${path} (${stats?.size ?? 'unknown'} bytes)`);
  });

  const additions = await watcher.getObservableFor('add');
  additions.subscribe(([path]) => {
    console.log(`New file: ${path}`);
  });

  const deletions = await watcher.getObservableFor('unlink');
  deletions.subscribe(([path]) => {
    console.log(`Deleted: ${path}`);
  });

  // Handle graceful shutdown
  process.on('SIGINT', async () => {
    await watcher.stop();
    process.exit(0);
  });
}

watchProject();

API Reference

Smartwatch

Constructor

new Smartwatch(patterns: string[], options?: ISmartwatchOptions)

Creates a new Smartwatch instance with the given glob patterns.

Parameters:

• patterns — Array of glob patterns to watch (e.g., ['./src/**/*.ts', './config/*.json']); relative patterns resolve against the working directory, and a path without glob characters watches that file or directory tree
• options — Optional settings:

| Option | Type | Default | Description | |------------------|----------|---------|-------------| | startTimeoutMs | number | 30000 | How long start() may take to complete its initial scan before it rejects with SmartwatchStartTimeoutError, in milliseconds. A positive integer up to 2147483647; any other value makes the constructor throw a RangeError. |

Methods

| Method | Returns | Description | |----------------------------------------|------------------------------------------------|------------------------------------------------| | start() | Promise<void> | Starts watching; resolves once the initial scan is complete, rejects with a SmartwatchError if it cannot | | stop() | Promise<void> | Stops the file watcher and cleans up resources; cancels a running start() | | add(patterns: string[]) | void | Adds additional patterns to watch | | remove(pattern: string) | void | Removes a pattern from the watch list | | getObservableFor(event: TFsEvent) | Promise<Observable<[string, Stats \| undefined]>> | Returns an RxJS observable for the specified event; resolves at once |

Properties

| Property | Type | Description | |----------|-------------------------------------------|--------------------------| | status | 'idle' \| 'starting' \| 'watching' | Current watcher status |

Types

type TFsEvent = 'add' | 'addDir' | 'change' | 'error' | 'unlink' | 'unlinkDir' | 'ready' | 'raw';
type TSmartwatchStatus = 'idle' | 'starting' | 'watching';

interface ISmartwatchOptions {
  startTimeoutMs?: number; // default 30000
}

class SmartwatchError extends Error {}
class SmartwatchStoppedError extends SmartwatchError {}
class SmartwatchStartTimeoutError extends SmartwatchError { readonly timeoutMs: number }
class SmartwatchScanError extends SmartwatchError {} // cause: the scan error

Requirements

| Runtime | Version | |-----------------|----------------------------------------| | Node.js | 20+ | | Deno | Any version with Deno.watchFs() support | | Bun | Uses Node.js compatibility layer |

License and Legal Information

This repository contains open-source code licensed under the MIT License. A copy of the license can be found in the LICENSE file.

Please note: The MIT License does not grant permission to use the trade names, trademarks, service marks, or product names of the project, except as required for reasonable and customary use in describing the origin of the work and reproducing the content of the NOTICE file.

Trademarks

This project is owned and maintained by Task Venture Capital GmbH. The names and logos associated with Task Venture Capital GmbH and any related products or services are trademarks of Task Venture Capital GmbH or third parties, and are not included within the scope of the MIT license granted herein.

Use of these trademarks must comply with Task Venture Capital GmbH's Trademark Guidelines or the guidelines of the respective third-party owners, and any usage must be approved in writing. Third-party trademarks used herein are the property of their respective owners and used only in a descriptive manner, e.g. for an implementation of an API or similar.

Company Information

Task Venture Capital GmbH Registered at District Court Bremen HRB 35230 HB, Germany

For any legal inquiries or further information, please contact us via email at [email protected].

By using this repository, you acknowledge that you have read this section, agree to comply with its terms, and understand that the licensing of the code does not imply endorsement by Task Venture Capital GmbH of any derivative works.