p-limit vs p-map
Concurrency Control in JavaScript Comparison
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What's Concurrency Control in JavaScript?

Both p-limit and p-map are utility libraries in JavaScript that help manage concurrency when dealing with asynchronous operations. p-limit allows you to limit the number of concurrent promises, ensuring that you do not overwhelm your system or API with too many requests at once. On the other hand, p-map extends this functionality by allowing you to map over an array of items while controlling the concurrency, making it easier to process multiple items asynchronously without exceeding a specified limit. These libraries are particularly useful in scenarios where you need to perform multiple asynchronous tasks, such as API calls or file operations, while maintaining control over the number of simultaneous executions.

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p-limit159,148,0162,36110.3 kB96 months agoMIT
p-map53,711,6991,42621.2 kB126 months agoMIT
Feature Comparison: p-limit vs p-map

Concurrency Control

  • p-limit:

    p-limit provides a simple way to limit the number of concurrent executions of a function. You can specify the maximum number of promises that can run at the same time, which helps prevent resource exhaustion and improves performance by avoiding bottlenecks. This is particularly useful when making API requests or performing I/O operations that can be limited by external constraints.

  • p-map:

    p-map allows you to process an array of items with a mapping function while controlling the concurrency. It combines the functionality of mapping and concurrency control, enabling you to apply a transformation to each item in the array while ensuring that only a specified number of promises are executed concurrently. This is beneficial when you need to transform data fetched from an API without overwhelming the server.

Ease of Use

  • p-limit:

    p-limit is designed to be simple and easy to use. You can quickly set up a limit on concurrent executions with minimal configuration, making it accessible for developers who need a straightforward solution for concurrency management.

  • p-map:

    p-map is also user-friendly, but it requires a bit more setup since you need to provide both the mapping function and the array to process. However, once set up, it streamlines the process of handling asynchronous transformations with concurrency control.

Performance Optimization

  • p-limit:

    By limiting the number of concurrent operations, p-limit can help optimize performance by reducing the load on your system and avoiding potential throttling from external services. This can lead to faster overall execution times when dealing with large sets of asynchronous tasks.

  • p-map:

    p-map optimizes performance by allowing you to control how many items are processed at once, which can lead to more efficient use of resources. It helps balance the workload and ensures that your application remains responsive while processing data.

Error Handling

  • p-limit:

    p-limit allows for error handling within the limited concurrent executions. If one promise fails, it does not affect the others, and you can handle errors as they occur without stopping the entire process.

  • p-map:

    p-map also supports error handling, allowing you to catch and manage errors for each individual mapping operation. This feature is crucial when processing multiple items, as it ensures that one failure does not halt the entire mapping process.

Use Cases

  • p-limit:

    p-limit is ideal for scenarios where you need to control the number of concurrent requests, such as when scraping data from multiple web pages or making bulk API calls. It is particularly useful in situations where the external service has rate limits.

  • p-map:

    p-map is best suited for cases where you need to transform data while fetching it asynchronously, such as processing a list of user IDs to retrieve user details from an API. It allows you to efficiently manage both the data retrieval and transformation in a controlled manner.

How to Choose: p-limit vs p-map
  • p-limit:

    Choose p-limit if you only need to limit the number of concurrent executions of a single asynchronous function without needing to transform the input data. It is lightweight and straightforward, making it ideal for simple use cases where you want to prevent overwhelming resources.

  • p-map:

    Choose p-map if you need to process an array of items asynchronously while also applying a transformation function to each item. It provides a convenient way to handle both mapping and concurrency control in one go, making it suitable for more complex scenarios where you want to manipulate data as you process it.

Similar Npm Packages to p-limit

p-limit is a utility library that allows developers to limit the number of concurrent promises that can be executed at a time. This is particularly useful when dealing with APIs or other asynchronous operations where you want to avoid overwhelming the server or hitting rate limits. By using p-limit, you can control the flow of asynchronous tasks, ensuring that only a specified number of them run concurrently, while the others wait in line until a slot becomes available.

While p-limit is a great tool for managing concurrency, there are other libraries that provide similar functionality. Here are a couple of alternatives:

  • p-queue is a promise queue that allows you to manage the concurrency of asynchronous tasks. It provides a more feature-rich solution than p-limit, with options for prioritizing tasks, setting a maximum concurrency level, and even handling retries. If you need more control over the order and execution of your asynchronous operations, p-queue is an excellent choice. It’s particularly useful for scenarios where you need to manage complex workflows or prioritize certain tasks over others.

  • p-throttle is another alternative that focuses on limiting the rate at which a function can be called. Unlike p-limit, which limits concurrent executions, p-throttle allows you to control how often a function can be invoked over time. This can be particularly useful for scenarios like API rate limiting, where you want to ensure that a function is not called too frequently. If your primary concern is controlling the rate of function execution rather than managing concurrency, p-throttle is the right tool for the job.

To see how p-limit compares with p-queue and p-throttle, check out the comparison: Comparing p-limit vs p-queue vs p-throttle.

Similar Npm Packages to p-map

p-map is a utility library for mapping over asynchronous operations in a more manageable way. It allows developers to run multiple promises concurrently while controlling the number of promises that are executed at any given time. This makes it particularly useful for scenarios where you need to perform multiple asynchronous tasks without overwhelming the system or the API being called. With p-map, you can specify a concurrency limit, ensuring that only a certain number of promises are processed simultaneously, which helps in optimizing resource usage and improving performance.

While p-map is a great tool for handling concurrent asynchronous operations, there are several alternatives that provide similar functionalities. Here are a few noteworthy alternatives:

  • p-all is a utility that allows you to run multiple promises in parallel and returns a single promise that resolves when all of the promises have resolved. Unlike p-map, which focuses on mapping over an array with concurrency control, p-all is straightforward and simply executes all promises at once. This can be useful when you want to wait for multiple asynchronous operations to complete without worrying about limiting the number of concurrent executions.

  • p-queue is a promise queue that allows you to manage the execution of asynchronous tasks with fine-grained control. It provides features such as concurrency limits, priority levels, and the ability to pause and resume the queue. p-queue is particularly useful when you need to manage a large number of asynchronous tasks and want to ensure that they are executed in a controlled manner, making it a powerful alternative to p-map for more complex scenarios.

  • p-series is a utility that runs promises in series, meaning that it waits for each promise to resolve before starting the next one. This is different from p-map, which allows for concurrent execution. If your use case requires that tasks be executed one after another rather than in parallel, p-series is the appropriate choice.

To explore how these packages compare, check out the following link: Comparing p-all vs p-map vs p-queue vs p-series.

README for p-limit

p-limit

Run multiple promise-returning & async functions with limited concurrency

Works in Node.js and browsers.

Install

npm install p-limit

Usage

import pLimit from 'p-limit';

const limit = pLimit(1);

const input = [
	limit(() => fetchSomething('foo')),
	limit(() => fetchSomething('bar')),
	limit(() => doSomething())
];

// Only one promise is run at once
const result = await Promise.all(input);
console.log(result);

API

pLimit(concurrency) default export

Returns a limit function.

concurrency

Type: number
Minimum: 1

Concurrency limit.

limit(fn, ...args)

Returns the promise returned by calling fn(...args).

fn

Type: Function

Promise-returning/async function.

args

Any arguments to pass through to fn.

Support for passing arguments on to the fn is provided in order to be able to avoid creating unnecessary closures. You probably don't need this optimization unless you're pushing a lot of functions.

limit.activeCount

The number of promises that are currently running.

limit.pendingCount

The number of promises that are waiting to run (i.e. their internal fn was not called yet).

limit.clearQueue()

Discard pending promises that are waiting to run.

This might be useful if you want to teardown the queue at the end of your program's lifecycle or discard any function calls referencing an intermediary state of your app.

Note: This does not cancel promises that are already running.

limit.concurrency

Get or set the concurrency limit.

limitFunction(fn, options) named export

Returns a function with limited concurrency.

The returned function manages its own concurrent executions, allowing you to call it multiple times without exceeding the specified concurrency limit.

Ideal for scenarios where you need to control the number of simultaneous executions of a single function, rather than managing concurrency across multiple functions.

import {limitFunction} from 'p-limit';

const limitedFunction = limitFunction(async () => {
	return doSomething();
}, {concurrency: 1});

const input = Array.from({length: 10}, limitedFunction);

// Only one promise is run at once.
await Promise.all(input);

fn

Type: Function

Promise-returning/async function.

options

Type: object

concurrency

Type: number
Minimum: 1

Concurrency limit.

FAQ

How is this different from the p-queue package?

This package is only about limiting the number of concurrent executions, while p-queue is a fully featured queue implementation with lots of different options, introspection, and ability to pause the queue.

Related

  • p-throttle - Throttle promise-returning & async functions
  • p-debounce - Debounce promise-returning & async functions
  • p-all - Run promise-returning & async functions concurrently with optional limited concurrency
  • More…
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