Run multiple promise-returning & async functions with limited concurrency
Run multiple promise-returning & async functions with limited concurrency
Run multiple promise-returning & async functions with limited concurrency
Works in Node.js and browsers.
npm install p-limit
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);
Returns a limit function.
Type: number | object
Minimum: 1
Concurrency limit.
You can pass a number or an options object with a concurrency property.
Type: boolean
Default: false
Reject pending promises with an AbortError when clearQueue() is called.
This is recommended if you await the returned promises, for example with Promise.all, so pending tasks do not remain unresolved after clearQueue().
import pLimit from 'p-limit';
const limit = pLimit({concurrency: 1});
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.
Warning: Avoid calling the same limit function inside a function that is already limited by it. This can create a deadlock where inner tasks never run. Use a separate limiter for inner tasks.
Process an iterable of inputs with limited concurrency.
The mapper function receives the item value and its index.
Returns a promise equivalent to Promise.all(Array.from(iterable, (item, index) => limit(mapperFunction, item, index))).
This is a convenience function for processing inputs that arrive in batches. For more complex use cases, see p-map.
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).
Discard pending promises that are waiting to run.
This might be useful if you want to tear down 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.
When rejectOnClear is enabled, pending promises are rejected with an AbortError.
This is recommended if you await the returned promises, for example with Promise.all, so pending tasks do not remain unresolved after clearQueue().
Get or set the concurrency limit.
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);
Type: Function
Promise-returning/async function.
Type: object
Type: number
Minimum: 1
Concurrency limit.
Type: boolean
Default: false
Reject pending promises with an AbortError when clearQueue() is called.
This is recommended if you await the returned promises, for example with Promise.all, so pending tasks do not remain unresolved after clearQueue().
Discard pending calls that have not started yet.
When rejectOnClear is enabled, pending promises are rejected with an AbortError. Otherwise, their promises remain unresolved.
This does not cancel calls that are already running.
See recipes.md for common use cases and patterns.
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.
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