p-limit
Limit concurrency when running multiple promise-returning and async functions in Node.js and browsers.
What is p-limit?
p-limit is a JavaScript library that limits the concurrency of promise-returning and async functions. It solves the problem of resource exhaustion by ensuring only a specified number of tasks run simultaneously, which is crucial for managing API calls, database queries, or any async operations where uncontrolled parallelism can cause performance issues.
JavaScript developers working in Node.js or browser environments who need to manage concurrent async operations, such as handling rate-limited APIs, controlling database connection pools, or optimizing resource usage in performance-critical applications.
Developers choose p-limit for its minimalistic, focused approach to concurrency control without the overhead of full queue implementations. It's lightweight, easy to integrate, and provides essential features like queue clearing and convenience methods while maintaining cross-platform compatibility.
Overview
Run multiple promise-returning & async functions with limited concurrency
Use Cases
Best For
- Limiting concurrent API requests to avoid rate limiting
- Controlling database query concurrency to prevent connection pool exhaustion
- Managing file I/O operations in Node.js to reduce system load
- Throttling async tasks in browser applications to improve performance
- Processing batches of data with controlled parallelism
- Replacing manual Promise.all implementations with built-in concurrency limits
Not Ideal For
- Projects needing advanced queue features like task prioritization or pause/resume functionality
- Scenarios where cancellation of actively running promises is required – clearQueue only handles pending tasks
- Complex workflows with task dependencies or conditional execution – p-limit only manages concurrency without scheduling logic
Pros & Cons
Pros
Offers a straightforward API with core functions like pLimit and limit.map, making integration quick and reducing cognitive load, as shown in the simple usage example.
Provides activeCount and pendingCount for real-time monitoring and clearQueue for cleanup, with rejectOnClear option to handle pending promises cleanly using AbortError.
Includes limit.map() for batch processing and limitFunction() for scoping concurrency to a single function, reducing boilerplate for common use cases.
Works in both Node.js and browser environments, ensuring versatility across different JavaScript runtimes without platform-specific adjustments.
Cons
The README explicitly warns that calling the same limit function inside a limited function can cause deadlocks, requiring careful design or separate limiters for nested tasks.
Lacks advanced queue features like prioritization, event emission, or pausing, making it unsuitable for complex scheduling, as acknowledged in the FAQ comparison with p-queue.
clearQueue() only discards pending promises and cannot cancel or abort promises that are already running, which may be insufficient for dynamic or error-prone environments.
Frequently Asked Questions
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