await-reduce

Resolve and reduce an array of promises

const reduce = require('await-reduce');

The behaviour matches Array.prototype.reduce.

const results = await reduce(
	[
		fetch('one').then(res => res.json()),
		fetch('two').then(res => res.json()),
		fetch('ten').then(res => res.json()),
	],
	(accumulator, item) => [...accumulator, item],
	[]
)

The callback matches Array.prototype.reduce's 4 argument signature, except the 4th argument (array) are the results of the Promises, and the callback itself can be asynchronous as well.

const results = await reduce(
	[
		fetch('one'),
		fetch('two'),
		fetch('ten'),
	],
	async (accumulator, response, index, array) => {
		if (!response.ok) {
			return accumulator
		}
		const data = await response.json()
		return Object.assign(accumulator, data)
	},
	{}
)

Transpiled version

Environments which exclude node_modules from the transpiling pipeline should include the "browser" entry instead of "main". This exposes an ES5 commonjs module.

Also available for explicit import:

const reduce = require('await-reduce/dist');