p-reduce

What is p-reduce?

The p-reduce npm package is a utility that allows you to reduce a list of values using promises in series. It is particularly useful when you need to perform a series of asynchronous operations in sequence and combine their results into a single value.

What are p-reduce's main functionalities?

Promise Reduction

This feature allows you to reduce an array of promises to a single promise that resolves to a value. The code sample demonstrates how to sum a series of numbers wrapped in promises.

const pReduce = require('p-reduce');
const promiseArray = [Promise.resolve(1), Promise.resolve(2), Promise.resolve(3)];
pReduce(promiseArray, (total, value) => Promise.resolve(total + value), 0).then(result => console.log(result)); // 6

Other packages similar to p-reduce

bluebird

Bluebird is a comprehensive promise library that includes a 'reduce' method similar to p-reduce. It offers additional features like cancellation, progress updates, and more efficient performance in some cases.

async

Async is a utility module which provides straight-forward, powerful functions for working with asynchronous JavaScript. It includes 'reduce' and 'reduceRight' functions that work with async operations, but it's not promise-based by default.

q

Q is a promise library that includes a 'reduce' method for promises. It is similar to p-reduce but also includes other features like making functions return promises and utilities for handling groups of promises.

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

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 - Iterate over promises serially
• p-map-series - Map over promises serially
• p-map - Map over promises concurrently
• More…

---

Get professional support for this package with a Tidelift subscription
_{Tidelift helps make open source sustainable for maintainers while giving companies
assurances about security, maintenance, and licensing for their dependencies.}