concurrentMap()

concurrentMap<Input, Output, ErrorOutput>(options, mapper, errorMapper?): ConcurrentMap<Input, Output, ErrorOutput>

Defined in: src/ConcurrentMap.ts:204

Creates an operator like map that runs up to options.concurrency mapper calls at the same time.

Results are emitted in the order the calls complete, which is not necessarily the order of the input.

If mapper throws and an errorMapper is given, its return value is emitted instead.

The operator starts working when the iteration starts, not when it is applied. If the source throws, or mapper throws and no errorMapper is given (or errorMapper throws), the iteration ends with that error: no new calls are started and the results of calls still running are discarded.

Type Parameters

Input

Input

Output

Output

ErrorOutput

ErrorOutput = never

Parameters

options

ConcurrentMapOptions

see ConcurrentMapOptions

mapper

(req) => Output | Promise<Output>

transforms an item; may be asynchronous

errorMapper?

(req, error) => ErrorOutput | Promise<ErrorOutput>

turns an error thrown by mapper into a value

Returns

ConcurrentMap<Input, Output, ErrorOutput>

an operator object

Example

import { setTimeout as sleep } from "node:timers/promises";

const delays = [60, 10, 30];
const work = async (ms: number) => {
    await sleep(ms);
    return ms;
};

await chain(delays).concurrentMap({ concurrency: 3 }, work).toArray();
// => [10, 30, 60]
await chain(delays).concurrentMap({ concurrency: 1 }, work).toArray();
// => [60, 10, 30]