Micro Utilities

Zero-dependency utilities for common TypeScript operations in dean-stack. Decision order — apply top-down, stop at the first match:

1. Native ECMAScript / Web API → use it (no install).
2. Bun.* built-in (tooling/scripts only — never in browser code).
3. One-line typed inline helper co-located with the call site.
4. just-* micro-package (bun add).
5. memoize-one for "cache the last call" — module scope only.

This is a cross-cutting authoring policy, not a tech. Anything that touches an owned dean-stack tech (state, storage, schemas, animation, canvas, routing, motion) defers to that tech's skill.

When to invoke

• Reaching for lodash, lodash-es, ramda, underscore, moment, or uuid — almost always there's a native or just-* answer.
• Manipulating objects (deep merge, deep clone, deep diff), arrays (group, partition, dedupe, sort, set ops), strings (case conversion, padding), numbers (clamp, format), or functions (debounce, throttle, memoize) in plain TS.
• Merging user input or generator answers over a defaults object.
• Choosing between useMemo and memoize-one for caching an expensive transform.

When NOT to invoke

• Schema validation → zod (Pillar 2). No Valibot, Yup, Joi, AJV.
• React state → jotai. No Zustand, Redux, Recoil, TanStack Query.
• Persistence → idb. No localForage, Dexie.
• Animation → animejs via useAnime.
• Canvas / 2D → pixijs via usePixiApp.
• Date arithmetic — no date library is pinned in dean-stack. Surface a stack-pin decision with the user before adding date-fns or anything else; Intl.DateTimeFormat covers display-only needs.

Owns

The decision order above, the native-first preference, the just-* adoption rules, the memoize-one-vs-Compiler call, and the anti-patterns that flag lodash / JSON.parse(JSON.stringify(…)) / moment / node-fetch / dotenv / bcrypt.

Defers to

• zod — every boundary input is parsed by a Zod schema; this skill does not validate.
• jotai — atom authoring + the atomWithIDB factory; state helpers live there.
• idb — IDB primitives + the root hydration promise; persistence helpers live there.
• react-compiler-rules — the "no manual useMemo / useCallback / React.memo" rule. memoize-one inside a component body is forbidden by that rule.
• react-19-primitives — useMemo / useTransition / useDeferredValue are the right answer when the cache is component-scoped.
• bun-runtime — the Bun.* API surface; tooling/scripts only, never in Vite-bundled browser code.
• bun-package-manager — for bun add invocations and the workspace packageManager pin.
• ts — strict-mode rules every helper must satisfy (noUncheckedIndexedAccess, exactOptionalPropertyTypes, verbatimModuleSyntax).
• biome — every helper file is linted; no exemption.

Dean-stack rules

• Pillar 4 (CLI-gate-first): every helper must compile under tsgo --noEmit strict and lint clean under Biome before bun run check will pass. No any, no as casts at module boundaries (Pillar 2 — parse with Zod instead).
• Bundle hygiene matters more than usual. Dean-stack ships static to GH Pages and reloads live on iPad over LAN. Prefer the native API or a 3-line inline helper over a 1KB just-* package; prefer a 1KB just-* package over a 70KB lodash import.
• Bun.* is browser-forbidden. Bun.deepEquals, Bun.escapeHTML, Bun.password, Bun.file, Bun.$, Bun.serve are tooling/scripts only (see bun-runtime). Vite bundles browser code; Bun.* symbols don't exist there. For browser code use the native column or write inline.
• Side-channel rule applies to debounce/throttle. just-debounce-it / just-throttle mutate captured-ref state across calls — same shape as anime.js / PixiJS (see react-compiler-rules). Hoist them to module scope or wrap in a useEffect-only pattern; never recreate the debounced function in render. Do NOT reach for useCallback to stabilize them — let the Compiler memoize the JSX and keep the function reference stable via module scope.
• memoize-one only at module scope. Inside a component, the Compiler memoizes; manual memoize-one is forbidden by Pillar 4. The legitimate use is const computeStyles = memoizeOne(buildStyles) once at the top of a file.
• No date library is pinned. Adding date-fns, dayjs, moment, or anything else is a stack-pin change — surface it with the user first. Display-only formatting goes through Intl.DateTimeFormat.

Patterns

Native-first reference (use these before any package)

Bun.* reference (tooling/scripts only — bun-runtime)

For Vite-bundled browser code (apps/web/app/...), use the native column or write a typed helper inline.

Type-safe helpers (preferred over just-pick / just-omit when types must stay precise)

export function pick<T extends object, K extends keyof T>(obj: T, keys: readonly K[]): Pick<T, K> {
  const result = {} as Pick<T, K>;
  for (const key of keys) if (key in obj) result[key] = obj[key];
  return result;
}

export function omit<T extends object, K extends keyof T>(obj: T, keys: readonly K[]): Omit<T, K> {
  const result = { ...obj };
  for (const key of keys) delete result[key];
  return result as Omit<T, K>;
}

export function groupBy<T, K extends PropertyKey>(
  arr: readonly T[],
  getKey: (item: T) => K,
): Partial<Record<K, T[]>> {
  return arr.reduce<Partial<Record<K, T[]>>>((acc, item) => {
    const key = getKey(item);
    (acc[key] ??= []).push(item);
    return acc;
  }, {});
}

export function dedupeBy<T, K>(arr: readonly T[], getKey: (item: T) => K): T[] {
  const seen = new Set<K>();
  return arr.filter((x) => {
    const k = getKey(x);
    if (seen.has(k)) return false;
    seen.add(k);
    return true;
  });
}

export function clamp(n: number, min: number, max: number): number {
  return Math.min(Math.max(n, min), max);
}

These compile clean under tsgo --noEmit strict. Co-locate with the call site; only promote to a shared file when ≥2 callers exist with identical signatures.

just-* packages — when to add

bun add <package>. Each is <1KB minified, zero deps. If two workspaces use the same just-*, pin via the root package.json so versions stay in sync (see bun-package-manager).

Dean-stack patterns

Deep clone an IDB record before mutating — structuredClone handles Date / Map / Set, which IDB records can contain. Never JSON.parse(JSON.stringify(...)).

Merge generator answers over template defaults (in turbo/generators/config.ts):

import extend from "just-extend";
const merged = extend(true, {}, templateDefaults, userAnswers);

Debounce a search input inside a route component — declare at module scope, not in the component body:

// At module scope.
import debounce from "just-debounce-it";
import { useSetAtom } from "jotai"; // see `jotai`
import { searchAtom } from "./atoms";

const queueSearch = debounce((query: string, set: (q: string) => void) => {
  set(query);
}, 300);

function SearchInput() {
  const setQuery = useSetAtom(searchAtom);
  return <input => queueSearch(e.target.value, setQuery)} />;
}

The Compiler memoizes the JSX; queueSearch is reference-stable because it's at module scope. Don't wrap in useCallback (see react-compiler-rules).

Module-scope memoize-one for an expensive transform:

import memoizeOne from "memoize-one";
const computeTokens = memoizeOne((mode: "light" | "dark", accent: string) => buildTokens(mode, accent));

Defined once at the top of a file. useMemo would re-cache per-component; module scope caches across the whole app.

Anti-patterns

• Don't JSON.parse(JSON.stringify(obj)) — drops Date / Map / Set / RegExp, throws on functions/symbols, breaks IDB records. Use structuredClone(obj).
• Don't import lodash / lodash-es — too heavy for the iPad-LAN budget; everything is now native or just-*.
• Don't import moment — not pinned in this stack; surface a date-library decision with the user first.
• Don't arr.sort() when you don't intend to mutate — use arr.toSorted().
• Don't use Bun.* in browser code — Vite bundles it and the symbol won't exist at runtime. Tooling/scripts only (see bun-runtime).
• Don't put memoize-one inside a component body — Compiler memoizes; manual memo is forbidden (see react-compiler-rules). Module scope is the only valid use.
• Don't recreate debounce(...) / throttle(...) in render — module scope or useEffect-mounted only. Same side-channel rule as anime.js / PixiJS.
• Don't reach for useCallback to stabilize a debounced function — hoist it to module scope; the Compiler handles the rest.
• Don't import node-fetch / cross-fetch — fetch is global on Bun and Node 21+.
• Don't import dotenv — Bun loads .env automatically; build-time vars go through t3-env.
• Don't import bcrypt / argon2 — there is no server in dean-stack; auth doesn't apply on GH Pages.
• Don't validate with anything other than Zod — Pillar 2; Valibot / Yup / Joi / AJV are forbidden (see zod).
• Don't grow a shared utils/ graveyard — co-locate small helpers with their call sites; only promote to a shared file when ≥2 callers exist with identical signatures.

Triggers on

structuredClone, deep clone, deep merge, deep equality, group by, partition, pick omit, debounce, throttle, memoize-one, just-extend, micro utilities, lodash alternative