# p-reduce

> Reduce a list of values using promises into a promise for a value

Latest version **3.0.0** (published 2021-04-08) · MIT license · 0 weekly downloads

## Install

```sh
npm install p-reduce
pnpm add p-reduce
yarn add p-reduce
bun add p-reduce
```

## Health

**Score 43/100 (D)** — status: abandoned.

Positive: has types package; esm support; no vulnerabilities; high maintenance score; high quality score.

Warnings: low downloads.

Negative: abandoned.

## Facts

| | |
|---|---|
| Version | 3.0.0 |
| Published | 2021-04-08 |
| First published | 2016-10-21 |
| Weekly downloads | 0 |
| License | MIT |
| TypeScript types | separate (@types/p-reduce) |
| Module format | ESM |
| Node | >=12 |
| Dependencies | 0 |
| Unpacked size | 5.8 KB |
| Known vulnerabilities | 0 |
| Install scripts | no |
| GitHub stars | 73 |
| Author | Sindre Sorhus |
| Maintainers | sindresorhus |
| Keywords | promise, reduce, collection, iterable, iterator, async, await, promises, accumulate, bluebird |

## Links

- npm: https://www.npmjs.com/package/p-reduce
- Repository: https://github.com/sindresorhus/p-reduce
- Homepage: https://github.com/sindresorhus/p-reduce#readme
- Issues: https://github.com/sindresorhus/p-reduce/issues
- Funding: https://github.com/sponsors/sindresorhus
- npm.io page: https://npm.io/package/p-reduce

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## Recent versions

- 3.0.0 (latest) — 2021-04-08
- 2.1.0 — 2019-04-04
- 2.0.0 — 2019-03-12
- 1.0.0 — 2016-10-21

## README

# p-reduce

> Reduce a list of values using promises into a promise for a value

Useful when you need to calculate some accumulated value based on async resources.

## Install

```
$ npm install p-reduce
```

## Usage

```js
import pReduce from 'p-reduce';
import humanInfo from 'human-info'; // Not a real module

const names = [
	getUser('sindresorhus').then(info => info.name),
	'Addy Osmani',
	'Pascal Hartig',
	'Stephen Sawchuk'
];

const totalAge = await pReduce(names, async (total, name) => {
	const info = await humanInfo(name);
	return total + info.age;
}, 0);

console.log(totalAge);
//=> 125
```

## API

### pReduce(input, reducer, initialValue?)

Returns a `Promise` that is fulfilled when all promises in `input` and ones returned from `reducer` are fulfilled, or rejects if any of the promises reject. The fulfilled value is the result of the reduction.

#### input

Type: `Iterable<Promise|any>`

Iterated over serially in the `reducer` function.

#### reducer(previousValue, currentValue, index)

Type: `Function`

Expected to return a value. If a `Promise` is returned, it's awaited before continuing with the next iteration.

#### initialValue

Type: `unknown`

Value to use as `previousValue` in the first `reducer` invocation.

## Related

- [p-each-series](https://github.com/sindresorhus/p-each-series) - Iterate over promises serially
- [p-map-series](https://github.com/sindresorhus/p-map-series) - Map over promises serially
- [p-map](https://github.com/sindresorhus/p-map) - Map over promises concurrently
- [More…](https://github.com/sindresorhus/promise-fun)

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---
_Source: https://npm.io/package/p-reduce · Machine-readable twin of the npm.io package page. Health data is recomputed on every publish._