p-map/index.d.ts

export interface Options {
	/**
	Number of concurrently pending promises returned by `mapper`.

	Must be an integer from 1 and up or `Infinity`.

	@default Infinity
	*/
	readonly concurrency?: number;

	/**
	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](https://github.com/sindresorhus/aggregate-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](https://github.com/sindresorhus/p-map/issues/51) can be implemented for abort control.

	@default true
	*/
	readonly stopOnError?: boolean;
}

/**
Function which is called for every item in `input`. Expected to return a `Promise` or value.

@param element - Iterated element.
@param index - Index of the element in the source array.
*/
export type Mapper<Element = any, NewElement = unknown> = (
	element: Element,
	index: number
) => NewElement | Promise<NewElement>;

/**
@param input - 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.
@param mapper - Function which is called for every item in `input`. Expected to return a `Promise` or value.
@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.

@example
```
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/']
```
*/
export default function pMap<Element, NewElement>(
	input: AsyncIterable<Element | Promise<Element>> | Iterable<Element | Promise<Element>>,
	mapper: Mapper<Element, NewElement>,
	options?: Options
): Promise<Array<Exclude<NewElement, typeof pMapSkip>>>;

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

@example
```
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/']
```
*/
export const pMapSkip: unique symbol;