Collections

Collection helpers apply an async function to each element of an array or object. They support optional concurrency limits and cancellation.

Import

import { map, filter, reduce, each } from "@vgerbot/async";

import { map, filter, reduce } from "@vgerbot/async/collections";

Array vs object input

All collection APIs accept both arrays and objects. For arrays, the callback receives (item, token). For objects, the callback receives (item, key, token).

// Array
map([1, 2, 3], async (n, token) => n * 2);

// Object
map({ a: 1, b: 2 }, async (v, k, token) => v * 2);

Concurrency

Most collection APIs accept a concurrency option to limit simultaneous operations:

map(items, async (item, token) => fetch(item.url), { concurrency: 5 });

APIs

API	Description
`map`	Transform each item, returning an array of results.
`each`	Iterate for side effects, no results collected.
`filter`	Keep items that pass an async predicate.
`reduce`	Sequentially accumulate a result.
`detect`	Find the first item matching a predicate.
`every`	Check if all items pass a predicate.
`some`	Check if any item passes a predicate.
`groupBy`	Group items by an async-computed key.
`sortBy`	Sort items by an async-computed key.
`concat`	Map and flatten results (flatMap).
`partition`	Split into two arrays by predicate.
`mapValues`	Transform object values, preserving keys.
`pick`	Filter object properties by predicate.
`omit`	Exclude object properties by predicate.
`transform`	Build a result with in-place mutation.
`reject`	Remove items matching a predicate.
`findIndex`	Find the index of the first matching item.