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Map over promises concurrently

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p-map

Map over promises concurrently

Useful when you need to run promise-returning & async functions multiple times with different inputs concurrently.

This is different from Promise.all() in that you can control the concurrency and also decide whether or not to stop iterating when there's an error.

Install

$ npm install p-map

Usage

import pMap from 'p-map';
import got from 'got';

const sites = [
	getWebsiteFromUsername('sindresorhus'), //=> Promise
	'https://avajs.dev',
	'https://github.com'
];

const mapper = async site => {
	const {requestUrl} = await got.head(site);
	return requestUrl;
};

const result = await pMap(sites, mapper, {concurrency: 2});

console.log(result);
//=> ['https://sindresorhus.com/', 'https://avajs.dev/', 'https://github.com/']

API

pMap(input, mapper, options?)

Returns a Promise that is fulfilled when all promises in input and ones returned from mapper are fulfilled, or rejects if any of the promises reject. The fulfilled value is an Array of the fulfilled values returned from mapper in input order.

input

Type: Iterable<Promise | unknown>

Iterated over concurrently in the mapper function.

mapper(element, index)

Type: Function

Expected to return a Promise or value.

options

Type: object

concurrency

Type: number (Integer)
Default: Infinity
Minimum: 1

Number of concurrently pending promises returned by mapper.

stopOnError

Type: boolean
Default: true

When set to false, instead of stopping when a promise rejects, it will wait for all the promises to settle and then reject with an aggregated error containing all the errors from the rejected promises.

pMapSkip

Return this value from a mapper function to skip including the value in the returned array.

import pMap, {pMapSkip} from 'p-map';
import got from 'got';

const sites = [
	getWebsiteFromUsername('sindresorhus'), //=> Promise
	'https://avajs.dev',
	'https://example.invalid',
	'https://github.com'
];

const mapper = async site => {
	try {
		const {requestUrl} = await got.head(site);
		return requestUrl;
	} catch {
		return pMapSkip
	}
};

const result = await pMap(sites, mapper, {concurrency: 2});

console.log(result);
//=> ['https://sindresorhus.com/', 'https://avajs.dev/', 'https://github.com/']

p-map for enterprise

Available as part of the Tidelift Subscription.

The maintainers of p-map and thousands of other packages are working with Tidelift to deliver commercial support and maintenance for the open source dependencies you use to build your applications. Save time, reduce risk, and improve code health, while paying the maintainers of the exact dependencies you use. Learn more.

Related

  • p-all - Run promise-returning & async functions concurrently with optional limited concurrency
  • p-filter - Filter promises concurrently
  • p-times - Run promise-returning & async functions a specific number of times concurrently
  • p-props - Like Promise.all() but for Map and Object
  • p-map-series - Map over promises serially
  • p-queue - Promise queue with concurrency control
  • More…
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Score

Popularity65/100
Quality84/100
Maintenance100/100