🔄 A lightweight and efficient Web Worker pool implementation for TypeScript/JavaScript applications.

• Object Pool Pattern: Reuses idle Web Workers to avoid the overhead of creating and destroying them
• Configurable Pool Behavior: Set initial worker count and idle pool capacity
• TypeScript Support: Full TypeScript definitions included
• Zero Dependencies: Lightweight with no external runtime dependencies
• Memory Efficient: Automatically terminates workers returned after the idle pool reaches capacity

npm install @seedgou/worker-pool

pnpm add @seedgou/worker-pool

yarn add @seedgou/worker-pool

import { WorkerPool } from "@seedgou/worker-pool";

const createWorker = () => new Worker("/workers/processor.js", { type: "module" });

// Create a worker pool from a zero-argument worker factory
const pool = new WorkerPool(createWorker, {
  initialWorkers: 2,
  maxWorkers: 5,
});

// Get a worker from the pool
const worker = pool.get();

// Use the worker
worker.postMessage({ type: "process", data: "Hello World" });

// Return the worker to the pool when done
pool.return(worker);

The main class for managing a pool of Web Workers.

new WorkerPool(workerConstructor, options?)

Parameters:

• workerConstructor: Zero-argument factory function that creates and returns a new Worker
• options (optional): Configuration object
  • initialWorkers (optional): Number of workers to create initially (default: 0)
  • maxWorkers (optional): Maximum number of idle workers to keep in the pool (default: Infinity)

Gets an idle worker from the pool. If the pool is empty, creates and returns a new worker immediately.

Returns: A Worker instance ready for use

Returns a worker to the pool for reuse. If the idle pool has reached maxWorkers, the worker will be terminated instead of being retained.

Parameters:

• worker: The worker to return to the pool

import { WorkerPool } from "@seedgou/worker-pool";

const createWorker = () => new Worker("/workers/echo.js", { type: "module" });

// Create a simple worker pool
const pool = new WorkerPool(createWorker);

// Get a worker and use it
const worker = pool.get();
worker.postMessage("Hello from main thread");

worker.onmessage = (event) => {
  console.log("Received:", event.data);
  // Return worker to pool when done
  pool.return(worker);
};

import { WorkerPool } from "@seedgou/worker-pool";

const createWorker = () => new Worker("/workers/processor.js", { type: "module" });

// Create a pool with initial workers and size limit
const pool = new WorkerPool(createWorker, {
  initialWorkers: 3, // Start with 3 workers
  maxWorkers: 10, // Keep up to 10 idle workers available for reuse
});

// The pool starts with 3 workers ready to use
const worker1 = pool.get(); // Gets one of the initial workers
const worker2 = pool.get(); // Gets another initial worker
const worker3 = pool.get(); // Gets the third initial worker
const worker4 = pool.get(); // Creates a new worker (pool was empty)

// Return workers when done
pool.return(worker1);
pool.return(worker2);
pool.return(worker3);
pool.return(worker4);

import { WorkerPool } from "@seedgou/worker-pool";

const createWorker = () => new Worker("/workers/processor.js", { type: "module" });

const pool = new WorkerPool(createWorker, {
  initialWorkers: 2,
  maxWorkers: 4,
});

async function runTask(task: string) {
  const worker = pool.get();

  try {
    return await new Promise((resolve, reject) => {
      worker.onmessage = (event) => resolve(event.data);
      worker.onerror = reject;
      worker.postMessage(task);
    });
  } finally {
    worker.onmessage = null;
    worker.onerror = null;
    pool.return(worker);
  }
}

for (const task of ["task1", "task2", "task3"]) {
  const result = await runTask(task);
  console.log("Task completed:", result);
}

Web Workers are expensive to create and destroy. A worker pool provides several benefits:

1. Performance: Reusing workers eliminates the overhead of worker creation/destruction
2. Memory Efficiency: Limits how many idle workers are retained for reuse
3. Resource Management: Automatically terminates workers returned after the idle pool is full
4. Scalability: Useful when tasks frequently borrow and return workers

maxWorkers does not cap the number of workers that can be active at the same time.

WorkerPool#get() always returns immediately. If no idle worker is available, it creates a new one. maxWorkers only controls how many returned workers are kept around for reuse.

If you need a hard concurrency limit for task execution, add your own queue, semaphore, or scheduler on top of WorkerPool.

• Node.js 20.19+ or 22.12+
• pnpm (recommended) or npm

# Install dependencies
pnpm install

# Build the project
pnpm build

# Run tests
pnpm test

# Run tests with coverage
pnpm coverage

# Lint code
pnpm lint

# Format code
pnpm format

• build: Compile TypeScript to JavaScript
• test: Run tests with Vitest
• coverage: Run tests with coverage report
• lint: Lint and fix code with Oxlint
• lint-check: Check linting with Oxlint
• format: Format the repository with Oxfmt
• format-check: Check formatting with Oxfmt
• type-check: Run TypeScript type checking

MIT License - see LICENSE file for details.

Contributions are welcome! Please feel free to submit a Pull Request.

• GitHub: https://github.com/rwv/worker-pool
• Issues: https://github.com/rwv/worker-pool/issues