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.
$ npm install p-map
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/']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.
Type: AsyncIterable<Promise<unknown> | unknown> | Iterable<Promise<unknown> | unknown>
Synchronous or asynchronous iterable that is iterated over concurrently, calling the mapper function for each element. Each iterated item is await'd before the mapper is invoked so the iterable may return a Promise that resolves to an item.
Asynchronous iterables (different from synchronous iterables that return Promise that resolves to an item) can be used when the next item may not be ready without waiting for an asynchronous process to complete and/or the end of the iterable may be reached after the asynchronous process completes. For example, reading from a remote queue when the queue has reached empty, or reading lines from a stream.
Type: Function
Expected to return a Promise or value.
Type: object
Type: number (Integer)
Default: Infinity
Minimum: 1
Number of concurrently pending promises returned by mapper.
Type: boolean
Default: true
When true, the first mapper rejection will be rejected back to the consumer.
When 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.
Caveat: When true, any already-started async mappers will continue to run until they resolve or reject. In the case of infinite concurrency with sync iterables, all mappers are invoked on startup and will continue after the first rejection. Issue #51 can be implemented for abort control.
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/']Available as part of the Tidelift Subscription.
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- 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 forMapandObject - p-map-series - Map over promises serially
- p-queue - Promise queue with concurrency control
- More…