p-map
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    5.5.0 • Public • Published

    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: 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.

    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 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.

    signal

    Type: AbortSignal

    You can abort the promises using AbortController.

    Requires Node.js 16 or later.

    import pMap from 'p-map';
    import delay from 'delay';
    
    const abortController = new AbortController();
    
    setTimeout(() => {
    	abortController.abort();
    }, 500);
    
    const mapper = async value => value;
    
    await pMap([delay(1000), delay(1000)], mapper, {signal: abortController.signal});
    // Throws AbortError (DOMException) after 500 ms.

    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…

    Install

    npm i p-map

    DownloadsWeekly Downloads

    38,660,762

    Version

    5.5.0

    License

    MIT

    Unpacked Size

    16.7 kB

    Total Files

    5

    Last publish

    Collaborators

    • sindresorhus