arraykit

Tiny, type-safe array utilities — chunk, groupBy, keyBy, countBy, uniqueBy, partition, sortBy, zip, range, and numeric helpers. Zero dependencies.

JavaScript got .flat(), .at(), and Object.groupBy — but you still reach for lodash the moment you need chunk, a stable multi-key sortBy, or keyBy. arraykit is that handful of everyday array helpers, tree-shakeable, fully typed, and zero-dependency — import only what you use.

import { chunk, groupBy, sortBy } from "@billdaddy/arraykit";

chunk([1, 2, 3, 4, 5], 2);                       // [[1, 2], [3, 4], [5]]
groupBy(users, (u) => u.role);                   // { admin: [...], user: [...] }
sortBy(users, (u) => u.lastName, (u) => u.age);  // stable, multi-key

Why arraykit?

• The missing helpers. chunk, groupBy, keyBy, countBy, uniqueBy, partition, sortBy, zip, range, plus sum/mean/minBy/maxBy.
• Pure & predictable. Nothing mutates its input; selectors get the index too.
• Stable, multi-key sortBy. Pass several selectors; ties fall through in order.
• Strong types. zip infers a tuple type, groupBy/keyBy return records, minBy/maxBy return T | undefined.
• Tree-shakeable. sideEffects: false, ESM + CJS, zero dependencies.

Install

npm install @billdaddy/arraykit
# or: pnpm add @billdaddy/arraykit  /  yarn add @billdaddy/arraykit  /  bun add @billdaddy/arraykit

Grouping & dedupe

import { chunk, groupBy, keyBy, countBy, partition, uniqueBy } from "@billdaddy/arraykit";

chunk([1, 2, 3, 4, 5], 2);                 // [[1, 2], [3, 4], [5]]
groupBy([1, 2, 3, 4], (n) => n % 2 ? "odd" : "even"); // { odd: [1,3], even: [2,4] }
keyBy([{ id: "a" }, { id: "b" }], (x) => x.id);       // { a: {...}, b: {...} }
countBy(["a", "b", "a"], (x) => x);        // { a: 2, b: 1 }
partition([1, 2, 3, 4], (n) => n % 2 === 0); // [[2, 4], [1, 3]]
uniqueBy([{ id: 1 }, { id: 1 }, { id: 2 }], (x) => x.id); // [{id:1}, {id:2}]
uniqueBy([1, 1, 2, 3]);                    // [1, 2, 3]  (identity)

Ordering

import { sortBy, zip, range } from "@billdaddy/arraykit";

sortBy(people, (p) => p.age);              // ascending, original untouched
sortBy(people, (p) => p.last, (p) => p.age); // last name, then age

zip([1, 2, 3], ["a", "b", "c"]);           // [[1,"a"], [2,"b"], [3,"c"]]

range(4);        // [0, 1, 2, 3]
range(2, 6);     // [2, 3, 4, 5]
range(0, 10, 2); // [0, 2, 4, 6, 8]
range(3, 0);     // [3, 2, 1]

Numerics

import { sum, sumBy, mean, minBy, maxBy } from "@billdaddy/arraykit";

sum([1, 2, 3]);                  // 6
sumBy(carts, (c) => c.total);    // total of totals
mean([2, 4, 6]);                 // 4
minBy(users, (u) => u.age);      // youngest (or undefined)
maxBy(users, (u) => u.age);      // oldest

mean([]) is NaN; minBy/maxBy of an empty array are undefined; ties keep the first occurrence.

Pairs well with

| Need | Use | | --- | --- | | Deep equal / clone of elements | equalkit | | Read/write nested fields by path | dotpathkit |

Contributors ✨

This project follows the all-contributors specification. Contributions of any kind are welcome — code, docs, bug reports, ideas, reviews! See the emoji key for how each contribution is recognized, and open a PR or issue to get involved.

Thanks goes to these wonderful people:

License

MIT © Tung Tran