parallel

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Basic usage

Like _.map but built specifically to run the async callback functions in parallel. The first argument is a limit of how many functions should be allowed to run at once. Async callback functions are supplied with three arguments. The first is the array item. The second is the index of the item in the array. And the third is the index of the queue in which the item is being processed. Returns an array of results.

import { parallel } from 'radash'

const userIds = [1, 2, 3, 4, 5, 6, 7, 8, 9]

// Will run the find user async function 3 times at maximum at any time
// starting another request when one of the 3 is freed
const users = await parallel(3, userIds, async (userId, index, queueIndex) => {
  return await api.users.find(userId)
})

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Errors

When all work is complete parallel will check for errors. If any occurred they will all be thrown in a single AggregateError that has an errors property that is all the errors that were thrown.

import { parallel, try as tryit } from 'radash'

const userIds = [1, 2, 3]

const [err, users] = await tryit(parallel)(3, userIds, async (userId) => {
  throw new Error(`No, I don\'t want to find user ${userId}`)
})

console.log(err) // => AggregateError
console.log(err.errors) // => [Error, Error, Error]
console.log(err.errors[1].message) // => No, I don't want to find user 2