p-limit
Advanced tools
Package description
The p-limit npm package is a utility that allows you to limit the number of promises that are running at the same time. It is useful for controlling concurrency when you have operations that can be run in parallel but you want to limit the number of these operations due to resource constraints.
Concurrency Limiting
This feature allows you to create a limit for how many promises are allowed to run at once. In the code sample, the limit is set to 1, meaning that `doSomething` and `doAnotherThing` will not run at the same time.
const pLimit = require('p-limit');
const limit = pLimit(1);
async function doSomething() {}
async function doAnotherThing() {}
// Only one promise will run at once
const result1 = limit(() => doSomething());
const result2 = limit(() => doAnotherThing());Queueing
This feature demonstrates how additional promises are queued when the limit is reached. In this example, only two promises will run concurrently, and the rest will wait in the queue.
const pLimit = require('p-limit');
const limit = pLimit(2);
const input = [
limit(() => fetchSomething('foo')),
limit(() => fetchSomething('bar')),
limit(() => doSomethingElse()),
];
// Only two promises will run at once, the rest will be queued
Promise.all(input).then(results => {
console.log(results);
});Bottleneck is a powerful rate limiter that allows you to limit the number of calls to a function. It can be used to throttle requests to an API or any other operation that needs to be rate-limited. It is more feature-rich than p-limit, providing priorities, clustering support, and more configuration options.
Async provides a collection of utilities for working with asynchronous JavaScript. While it offers functions like `async.parallelLimit` which can limit the number of asynchronous operations running in parallel, it is a more comprehensive toolkit for asynchronous control flow, including series, waterfall, and eachOf methods.
P-Queue is a promise queue with adjustable concurrency that supports priorities, timeouts, and pausing. It is similar to p-limit but offers a higher level of abstraction with a queue system, making it suitable for more complex scenarios where you need to manage the order and priority of tasks.
Readme
Run multiple promise-returning & async functions with limited concurrency
$ npm install p-limit
const pLimit = require('p-limit');
const limit = pLimit(1);
const input = [
limit(() => fetchSomething('foo')),
limit(() => fetchSomething('bar')),
limit(() => doSomething())
];
(async () => {
// Only one promise is run at once
const result = await Promise.all(input);
console.log(result);
})();
Returns a limit function.
Type: number
Minimum: 1
Concurrency limit.
Returns the promise returned by calling fn(...args).
Type: Function
Promise-returning/async function.
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.
The number of promises that are currently running.
The number of promises that are waiting to run (i.e. their internal fn was not called yet).
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 and clear the queue.
MIT © Sindre Sorhus
FAQs
Run multiple promise-returning & async functions with limited concurrency
The npm package p-limit receives a total of 62,911,838 weekly downloads. As such, p-limit popularity was classified as popular.
We found that p-limit demonstrated a healthy version release cadence and project activity because the last version was released less than a year ago. It has 1 open source maintainer collaborating on the project.
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