# minimal-promise-pool > A minimal library for managing multiple promise instances (promise pool). Latest version **6.0.3** (published 2026-07-03) · Apache-2.0 license · 0 weekly downloads ## Install ```sh npm install minimal-promise-pool pnpm add minimal-promise-pool yarn add minimal-promise-pool bun add minimal-promise-pool ``` ## Health **Score 75/100 (B)** — status: active. Positive: has types; esm support; no vulnerabilities; has provenance; recently updated; high maintenance score; high quality score. Warnings: low downloads. ## Facts | | | |---|---| | Version | 6.0.3 | | Published | 2026-07-03 | | First published | 2021-10-09 | | Weekly downloads | 0 | | License | Apache-2.0 | | TypeScript types | bundled | | Module format | ESM + CommonJS | | Node | >=24 | | Dependencies | 0 | | Unpacked size | 40.9 KB | | Known vulnerabilities | 0 | | Install scripts | no | | Provenance | attested (GitHub Actions) | | GitHub stars | 2 | | Author | WillBooster Inc. | | Maintainers | exkazuu | | Keywords | async, promise, promise-pool | ## Links - npm: https://www.npmjs.com/package/minimal-promise-pool - Repository: https://github.com/WillBooster/minimal-promise-pool - Homepage: https://github.com/WillBooster/minimal-promise-pool#readme - Issues: https://github.com/WillBooster/minimal-promise-pool/issues - npm.io page: https://npm.io/package/minimal-promise-pool ## Alternatives - [@commercetools/sync-actions](https://npm.io/package/@commercetools/sync-actions.md) — 25.1K weekly downloads - [cwait](https://npm.io/package/cwait.md) — 21.4K weekly downloads - [@ledgerhq/hw-app-cosmos](https://npm.io/package/@ledgerhq/hw-app-cosmos.md) — 4.2K weekly downloads - [@financial-times/o-loading](https://npm.io/package/@financial-times/o-loading.md) — 2.8K weekly downloads - [fa](https://npm.io/package/fa.md) — 185 weekly downloads ## Recent versions - 6.0.3 (latest) — 2026-07-03 - 6.0.2 — 2026-04-18 - 6.0.1 — 2025-12-06 - 6.0.0 — 2025-11-05 - 5.0.0 — 2025-06-07 - 4.1.3 — 2025-06-07 - 4.1.2 — 2024-10-20 - 4.1.1 — 2024-06-23 - 4.1.0 — 2024-06-23 - 4.0.0 — 2023-09-14 - 3.0.3 — 2023-08-26 - 3.0.2 — 2023-08-11 - 3.0.1 — 2023-07-10 - 3.0.0 — 2023-07-10 - 2.1.13 — 2023-06-18 - … 22 more at https://npm.io/package/minimal-promise-pool/versions ## README # minimal-promise-pool [![Test](https://github.com/WillBooster/minimal-promise-pool/actions/workflows/test.yml/badge.svg)](https://github.com/WillBooster/minimal-promise-pool/actions/workflows/test.yml) [![npm version](https://img.shields.io/npm/v/minimal-promise-pool.svg)](https://www.npmjs.com/package/minimal-promise-pool) [![license](https://img.shields.io/npm/l/minimal-promise-pool.svg)](https://github.com/WillBooster/minimal-promise-pool/blob/main/LICENSE) [![semantic-release](https://img.shields.io/badge/%20%20%F0%9F%93%A6%F0%9F%9A%80-semantic--release-e10079.svg)](https://github.com/semantic-release/semantic-release) A minimal, zero-dependency promise pool for limiting the number of concurrently running promises. For example, `new PromisePool(2)` runs at most two tasks at the same time and queues the rest. ## Features - **Minimal** — a single class with no runtime dependencies. - **Typed** — written in TypeScript with full type definitions. - **Dual package** — ships both ESM and CommonJS builds. - **FIFO scheduling** — queued tasks start in the order they were submitted. - **Adjustable concurrency** — change the limit at runtime; the pool adapts immediately. ## Installation ```sh npm install minimal-promise-pool # or yarn add minimal-promise-pool ``` ## Quick Start The following example runs at most two tasks concurrently: ```ts import { PromisePool } from 'minimal-promise-pool'; const sleep = (ms: number) => new Promise((resolve) => setTimeout(resolve, ms)); const promisePool = new PromisePool(2); await promisePool.run(async () => { console.log('First task started'); await sleep(10_000); console.log('First task finished'); }); await promisePool.run(async () => { console.log('Second task started'); await sleep(10_000); console.log('Second task finished'); }); await promisePool.run(async () => { console.log('Third task started'); await sleep(10_000); console.log('Third task finished'); }); ``` Output: ``` First task started Second task started # ... about 10 seconds ... First task finished Third task started Second task finished # ... about 10 seconds ... Third task finished ``` Note that `run()` resolves when the task **starts**, not when it finishes. `await promisePool.run(...)` therefore applies backpressure: it pauses the caller only while the pool is full. ## Usage ### Getting a task's return value Use `runAndWaitForReturnValue()` when you need the task's result (or its error): ```ts const promisePool = new PromisePool(5); const results = await Promise.all( urls.map((url) => promisePool.runAndWaitForReturnValue(async () => (await fetch(url)).json())) ); ``` ### Waiting for all running tasks ```ts // Waits for all currently running tasks; rejects if any of them fails. await promisePool.promiseAll(); // Waits for all currently running tasks and collects each outcome. const outcomes = await promisePool.promiseAllSettled(); ``` ### Adjusting concurrency at runtime ```ts const promisePool = new PromisePool(10); promisePool.concurrency = 2; // Running tasks continue; new tasks respect the new limit. promisePool.concurrency = 20; // Queued tasks start immediately up to the new limit. ``` ## API ### `new PromisePool(concurrency = 10)` Creates a pool that runs at most `concurrency` tasks concurrently. ### Methods | Method | Returns | Description | | ---------------------------------------- | ------------------------------------ | ----------------------------------------------------------------------------------------- | | `run(startPromise)` | `Promise` | Runs the task when the pool has capacity. Resolves once the task has started. | | `runAndWaitForReturnValue(startPromise)` | `Promise` | Like `run()`, but resolves with the task's return value (and rejects if the task throws). | | `promiseAll()` | `Promise` | `Promise.all()` over the currently running tasks. | | `promiseAllSettled()` | `Promise[]>` | `Promise.allSettled()` over the currently running tasks. | ### Properties | Property | Type | Description | | --------------------- | -------- | ----------------------------------------------------------------------------------- | | `concurrency` | `number` | The maximum number of concurrent tasks. Writable; increasing it wakes queued tasks. | | `workingPromiseCount` | `number` | The number of currently running tasks. | | `queuedPromiseCount` | `number` | The number of tasks that have been submitted but not yet finished. | ### Error handling A rejection from a task passed to `run()` is not reported through `run()`'s returned promise (which only signals that the task started), and it becomes an unhandled promise rejection unless something else observes it. `promiseAll()` and `promiseAllSettled()` cover only the tasks still running at the moment of the call — a task that has already settled is removed from the pool, so a later call cannot collect its rejection. When you need task outcomes reliably, use `runAndWaitForReturnValue()` and collect the returned promises yourself: ```ts const outcomes = await Promise.allSettled(tasks.map((task) => promisePool.runAndWaitForReturnValue(task))); ``` ## License Apache License 2.0. See [LICENSE](LICENSE) and [NOTICE](NOTICE). --- _Source: https://npm.io/package/minimal-promise-pool · Machine-readable twin of the npm.io package page. Health data is recomputed on every publish._