p-map
- Version 7.0.2
- Published
- 21 kB
- No dependencies
- MIT license
Install
npm i p-map
yarn add p-map
pnpm add p-map
Overview
Map over promises concurrently
Index
Variables
Functions
Type Aliases
Variables
variable pMapSkip
const pMapSkip: Symbol;
Return this value from a
mapper
function to skip including the value in the returned array.Example 1
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/']
Functions
function pMap
pMap: <Element, NewElement>( input: | AsyncIterable<Element | Promise<Element>> | Iterable<Element | Promise<Element>>, mapper: Mapper<Element, NewElement>, options?: Options) => Promise<Array<Exclude<NewElement, typeof pMapSkip>>>;
Parameter input
Synchronous or asynchronous iterable that is iterated over concurrently, calling the
mapper
function for each element. Each iterated item isawait
'd before themapper
is invoked so the iterable may return aPromise
that resolves to an item. Asynchronous iterables (different from synchronous iterables that returnPromise
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.Parameter mapper
Function which is called for every item in
input
. Expected to return aPromise
or value.Returns
A
Promise
that is fulfilled when all promises ininput
and ones returned frommapper
are fulfilled, or rejects if any of the promises reject. The fulfilled value is anArray
of the fulfilled values returned frommapper
ininput
order.Example 1
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/']
function pMapIterable
pMapIterable: <Element, NewElement>( input: | AsyncIterable<Element | Promise<Element>> | Iterable<Element | Promise<Element>>, mapper: Mapper<Element, NewElement>, options?: IterableOptions) => AsyncIterable<Exclude<NewElement, typeof pMapSkip>>;
Parameter input
Synchronous or asynchronous iterable that is iterated over concurrently, calling the
mapper
function for each element. Each iterated item isawait
'd before themapper
is invoked so the iterable may return aPromise
that resolves to an item. Asynchronous iterables (different from synchronous iterables that returnPromise
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.Parameter mapper
Function which is called for every item in
input
. Expected to return aPromise
or value.Returns
An async iterable that streams each return value from
mapper
in order.Example 1
import {pMapIterable} from 'p-map';// Multiple posts are fetched concurrently, with limited concurrency and backpressurefor await (const post of pMapIterable(postIds, getPostMetadata, {concurrency: 8})) {console.log(post);};
Type Aliases
type BaseOptions
type BaseOptions = { /** Number of concurrently pending promises returned by `mapper`.
Must be an integer from 1 and up or `Infinity`.
@default Infinity */ readonly concurrency?: number;};
type IterableOptions
type IterableOptions = BaseOptions & { /** Maximum number of promises returned by `mapper` that have resolved but not yet collected by the consumer of the async iterable. Calls to `mapper` will be limited so that there is never too much backpressure.
Useful whenever you are consuming the iterable slower than what the mapper function can produce concurrently. For example, to avoid making an overwhelming number of HTTP requests if you are saving each of the results to a database.
Default: `options.concurrency` */ readonly backpressure?: number;};
type Mapper
type Mapper<Element = any, NewElement = unknown> = ( element: Element, index: number) => MaybePromise<NewElement | typeof pMapSkip>;
Function which is called for every item in
input
. Expected to return aPromise
or value.Parameter element
Iterated element.
Parameter index
Index of the element in the source array.
type MaybePromise
type MaybePromise<T> = T | Promise<T>;
type Options
type Options = BaseOptions & { /** 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 [`AggregateError`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/AggregateError) 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](https://github.com/sindresorhus/p-map/issues/51) can be implemented for abort control.
@default true */ readonly stopOnError?: boolean;
/** You can abort the promises using [`AbortController`](https://developer.mozilla.org/en-US/docs/Web/API/AbortController).
@example ``` 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. ``` */ readonly signal?: AbortSignal;};
Package Files (1)
Dependencies (0)
No dependencies.
Dev Dependencies (8)
Peer Dependencies (0)
No peer dependencies.
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