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. 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 at a time
// starting another request when one of the 3 is freed
const users = await parallel(3, userIds, async (userId) => {
  return await api.users.find(userId)
})

By default parallel will pick from the array in reverse order. If you want to run the functions in the order they are in the array you can pass executeInOrder option in the 4th argument.

// Will run the find user async function 3 at a time
// starting at the beginning of the array
const users = await parallel(3, userIds, async (userId) => {
  return await api.users.find(userId)
}, {executeInOrder: true})

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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