@ahmetilhn/memofy

memofy

Memoization for JavaScript and TypeScript functions. Skips re-running expensive work when the arguments have already been seen.

• Zero dependencies. 2.2 KB gzipped, self-contained.
• Constant-time lookups. Arguments are serialised into a structural key, so a cache hit costs the same at 10 entries and at 50 000.
• Bounded by default. LRU eviction with an optional TTL, so a long-running app cannot leak memory through the cache.
• Correct on hard inputs. Circular references, NaN, -0, Map, Set, Date, RegExp, URL, typed arrays and class instances all key correctly.
• Works anywhere. ESM, CommonJS and UMD builds; SSR-safe; no framework coupling. React, Vue, Nuxt, Next, Svelte or plain <script>.
• 100% test coverage, enforced in CI across 182 tests.

Table of contents

• Requirements
• Installation
• Quick start
• When to use it
• API reference
  • new Memofy(params?)
  • memofy.memoize(fn, deps?, context?, options?)
  • memofy.clear() / memofy.init()
  • The memoized function
  • createKey(args)
  • Exported types
• Guides
  • Dependencies
  • Context and this
  • Async functions
  • Cache size and expiry
  • Custom keys with resolver
  • Debugging
• Framework integration
• How arguments are compared
• Performance
• Bundle size
• FAQ and troubleshooting
• Migrating from v2
• Contributing
• Releasing
• License

Requirements

Node.js 24 or newer. In the browser, any engine supporting ES2022 — every evergreen release since 2022.

Installation

npm install @ahmetilhn/memofy

yarn add @ahmetilhn/memofy

Quick start

import Memofy from "@ahmetilhn/memofy";

const memofy = new Memofy();

const slowSum = (a, b) => {
  // pretend this is expensive
  return a + b;
};

const sum = memofy.memoize(slowSum);

sum(1, 2); // runs slowSum
sum(1, 2); // returns the cached result

Named and CommonJS imports work too:

import { Memofy } from "@ahmetilhn/memofy";
const { Memofy } = require("@ahmetilhn/memofy");

Browser, no build step:

<script src="https://unpkg.com/@ahmetilhn/memofy"></script>
<script>
  const memofy = new memofy.Memofy();
</script>

When to use it

Memoization trades memory for time, and building the cache key is not free. Roughly:

See Performance for measured key-building costs.

API reference

new Memofy(params?)

Creates an isolated cache universe. Functions memoized by one instance never share results with another.

new Memofy(params?: MemofyParams)

const memofy = new Memofy({ maxSize: 500, ttl: 60_000 });

Invalid values fall back to the default rather than throwing: a negative maxSize, a non-numeric ttl or a non-boolean flag is ignored.

memofy.memoize(fn, deps?, context?, options?)

Returns a memoized copy of fn with the same call signature.

memoize<F extends AnyFunction>(
  fn: F,
  deps?: Dependencies,
  context?: ThisParameterType<F>,
  options?: MemoizeOptions<F>
): Memoized<F>

options accepts maxSize, ttl and cacheRejectedPromises — overriding the instance defaults — plus:

Each call to memoize creates its own cache. Memoizing the same function twice gives two independent caches:

const a = memofy.memoize(fn);
const b = memofy.memoize(fn);
a(1); // runs
b(1); // runs again — separate caches

memofy.clear() / memofy.init()

clear(): void
init(): void

clear() empties the caches of every function memoized by this instance. init() does the same and re-publishes window.__memofy__ when trace is on; calling it is optional, since the constructor already runs it.

memofy.clear(); // every memoized function starts cold again

Caches are held inside each memoized function's closure, so clear() runs in constant time regardless of how many functions exist, and a memoized function that goes out of scope takes its cache with it — nothing keeps it alive.

The memoized function

The returned function keeps fn's parameters and return type, and adds two members:

type Memoized<F> = OmitThisParameter<F> & {
  clear: () => void;
  readonly size: number;
};

const double = memofy.memoize((n) => n * 2);

double(1);
double(2);
double(1);

double.size; // 2 — distinct argument sets cached
double.clear(); // drop just this function's cache
double.size; // 0

this is removed from the signature because the context you pass to memoize is already bound — callers invoke it as a plain function.

createKey(args)

The key builder is exported for testing, debugging, or writing a resolver on top of it.

createKey(args: ArrayLike<unknown>): string

import { createKey } from "@ahmetilhn/memofy";

createKey([1, "a"]) === createKey([1, "a"]); // true
createKey([{ a: 1, b: 2 }]) === createKey([{ b: 2, a: 1 }]); // true — order-free
createKey([1]) === createKey(["1"]); // false — type-tagged

Throws a RangeError if the arguments nest deeper than 500 levels.

Exported types

import type {
  AnyFunction,
  Dependencies,
  Memoized,
  MemoizeOptions,
  MemofyParams,
} from "@ahmetilhn/memofy";

Guides

Dependencies

Pass deps to invalidate the cache when something outside the arguments changes — the same idea as React's useMemo.

const settings = { taxRate: 0.2 };

const total = memofy.memoize(
  (price) => price * (1 + settings.taxRate),
  [settings]
);

total(100); // 120 — runs
total(100); // 120 — cached

settings.taxRate = 0.1;
total(100); // 110 — dependency changed, so it runs again

A dependency change clears the whole cache for that function, not just the current arguments.

Array form vs getter form. An array is captured once, so it can only observe mutations inside the values it holds. To track a rebindable primitive, pass a getter — it is re-read on every call:

let taxRate = 0.2;

// Wrong: taxRate was copied into the array and can never change.
memofy.memoize(fn, [taxRate]);

// Right: re-read on every call.
memofy.memoize(fn, () => [taxRate]);

Dependencies are compared with the same structural rules as arguments, so objects, Maps and Dates all work.

Context and this

The third parameter binds this. Each memoize call has its own cache, so two contexts never share results.

function greet() {
  return `hi ${this.name}`;
}

const greetAda = memofy.memoize(greet, [], { name: "Ada" });
const greetGrace = memofy.memoize(greet, [], { name: "Grace" });

greetAda(); // "hi Ada"
greetGrace(); // "hi Grace"

For class instances, memoize in the constructor so each instance gets its own cache:

class Cart {
  constructor(items) {
    this.items = items;
    this.total = memofy.memoize(
      function () {
        return this.items.reduce((sum, item) => sum + item.price, 0);
      },
      [this.items],
      this
    );
  }
}

TypeScript checks the context against the function's this parameter:

function greet(this: { name: string }): string {
  return this.name;
}

memofy.memoize(greet, [], { name: "Ada" }); // ok
memofy.memoize(greet, [], { wrong: true }); // compile error

Async functions

A promise is cached like any other value, so concurrent calls with the same arguments share one in-flight request.

const loadUser = memofy.memoize(async (id) => {
  const response = await fetch(`/api/users/${id}`);
  return response.json();
});

await Promise.all([loadUser(1), loadUser(1)]); // one request

Rejected promises are evicted once they settle, so a transient failure does not poison that argument set for the process lifetime:

await loadUser(1); // network error → rejects, entry removed
await loadUser(1); // tries again

Set cacheRejectedPromises: true to keep failures cached — useful when the failure is deterministic and retrying is pointless.

Note that attaching the eviction handler marks the promise as handled, so an unawaited rejection will not raise an unhandled-rejection warning from memofy's side. Handle the promise you receive as you normally would.

Cache size and expiry

Every memoized function gets a bounded LRU cache — 1000 entries by default. Reading an entry marks it most-recently-used, so hot entries survive.

const run = memofy.memoize(fn, [], undefined, { maxSize: 50 });

for (let i = 0; i < 10_000; i++) run(i);
run.size; // 50

Opt out with maxSize: 0 (or Infinity) when you know the input space is small and bounded:

const memofy = new Memofy({ maxSize: 0 });

ttl expires entries by age. Expiry is evaluated lazily on read — memofy never schedules a timer, so it cannot keep a Node process alive or leak handles:

const rates = memofy.memoize(fetchRates, [], undefined, { ttl: 60_000 });

Custom keys with resolver

When a cheap discriminator already exists, skip structural serialisation entirely:

const render = memofy.memoize(
  (user) => expensiveTemplate(user),
  [],
  undefined,
  { resolver: (user) => `${user.id}:${user.updatedAt}` }
);

This is worth reaching for when:

• arguments are large (serialising a 100-element array costs ~3 µs),
• arguments contain getters with side effects,
• only part of the argument actually affects the result.

The resolver runs with the same context as the function, and TypeScript types its parameters from fn.

Debugging

hasLogs logs every cache hit:

const memofy = new Memofy({ hasLogs: true });
// memofy: "getTotal" returned a cached value. 42

trace exposes the instance in browsers so you can inspect or clear from the console:

new Memofy({ trace: true });
// window.__memofy__.clear()

Both are no-ops outside the browser, so leaving trace on will not break SSR.

Framework integration

memofy is framework-agnostic; there is nothing to install beyond the package.

React

Create the instance once, outside the component, and memoize outside render.

import Memofy from "@ahmetilhn/memofy";

const memofy = new Memofy();
const formatRows = memofy.memoize((rows, locale) =>
  expensiveFormat(rows, locale)
);

function Table({ rows, locale }) {
  return <tbody>{formatRows(rows, locale).map(renderRow)}</tbody>;
}

Unlike useMemo, the cache survives unmounts and is shared across components, which is the point when the same inputs recur. Use useMemo for per-component values tied to a render; use memofy for pure computations shared app-wide.

Vue / Nuxt (client side)

// composables/useFormatter.js
import Memofy from "@ahmetilhn/memofy";

const memofy = new Memofy();

export const formatPrice = memofy.memoize((cents, currency) =>
  new Intl.NumberFormat(currency).format(cents / 100)
);

Svelte

// lib/search.js
import Memofy from "@ahmetilhn/memofy";

const memofy = new Memofy({ maxSize: 200 });
export const search = memofy.memoize((query, items) => rank(query, items));

SSR: Nuxt, Next, and any Node server

A module-level instance is shared by every request in the same process. That is fine for pure functions of their arguments, and wrong for anything scoped to a user — one visitor would be served another's cached result.

For per-user work, create an instance per request:

// Next.js route handler
export async function GET(request) {
  const memofy = new Memofy(); // isolated to this request
  const loadOrders = memofy.memoize((userId) =>
    db.orders.findMany({ userId })
  );

  return Response.json(await loadOrders(getUserId(request)));
}

// Nuxt server route
export default defineEventHandler(async (event) => {
  const memofy = new Memofy();
  const loadCart = memofy.memoize((userId) => fetchCart(userId));

  return loadCart(await getUserId(event));
});

For process-wide caches of genuinely shared data, keep the module-level instance and set a ttl so entries do not go stale.

Plain JavaScript

<script type="module">
  import Memofy from "https://unpkg.com/@ahmetilhn/memofy/build/index.mjs";

  const memofy = new Memofy();
  const fib = memofy.memoize((n) => (n < 2 ? n : fib(n - 1) + fib(n - 2)));
  console.log(fib(35));
</script>

How arguments are compared

Arguments are serialised into a type-tagged structural key, which is what makes lookups constant-time and comparisons predictable:

Only own enumerable properties participate, including symbol keys.

Two caveats worth knowing:

• Building a key reads getters, so a getter with side effects will fire.
• If a key cannot be built — a getter throws, or nesting exceeds 500 levels — memofy calls the original function directly. You lose caching, never correctness.

Both are avoidable with a resolver.

Performance

node scripts/bench.mjs on Node 24, Apple Silicon:

Cache hit cost does not grow with cache size. Recency is tracked with a doubly-linked list rather than by re-inserting into a Map: V8 rehashes an ordered hash map on deletion, so the obvious delete + set promotion costs ~20 µs per read on a 10k-entry cache, while relinking two pointers stays flat.

Memoize functions that cost more than roughly a microsecond; below that, key building dominates.

Bundle size

ESM and CommonJS builds ship unminified with source maps for your bundler to process. The package is side-effect free and fully tree-shakeable — importing without using it leaves nothing behind.

Entry points:

FAQ and troubleshooting

My function still runs every time. Most often the arguments differ in a way you did not expect — a fresh callback or a Date created per call. createKey([...args]) on two calls tells you immediately whether they key the same. A deps getter returning a new object every call has the same effect.

Two different inputs return the same result. That should not happen. Every type is tagged and every payload length-prefixed precisely to avoid collisions. If you find one, it is a bug worth reporting.

Can I memoize a method and keep this? Yes — pass the instance as the third argument. See Context and this.

Does the cache leak memory? No. Every cache is bounded (1000 entries by default), holds no timers, and lives in the memoized function's closure, so dropping the function drops the cache. Passing maxSize: 0 opts into an unbounded cache; that one is on you.

Can I share a cache between two memoized functions? No, by design — that was the source of several v2 bugs. Memoize once and share the returned function.

Does it work with recursion? Yes, if the recursive call goes through the memoized name:

const fib = memofy.memoize((n) => (n < 2 ? n : fib(n - 1) + fib(n - 2)));

Is it safe in SSR? Yes, provided you scope instances correctly. See SSR.

Migrating from v2

v2 had defects that made memoization silently incorrect. The fixes change observable behaviour, hence the major version.

Required code changes:

- import { initMemofy } from "@ahmetilhn/memofy";
- const memofy = new Memofy();
+ import Memofy from "@ahmetilhn/memofy";
+ const memofy = new Memofy();

• initMemofy no longer exists; the constructor initialises the instance.
• npm uninstall @ahmetilhn/handy-utils unless you use it directly.
• If you relied on an unbounded cache, pass { maxSize: 0 }.
• If you depended on primitive deps never invalidating, that was a bug; use the getter form to track them.

Contributing

npm install
npm run verify   # typecheck, test with coverage, build, bundle-size budget
npm run bench    # performance numbers

182 tests, enforced at 100% for statements, branches, functions and lines.

Releasing

Releases are automatic. Bump version in package.json and merge to master:

npm version patch   # or minor / major
git push origin master

The publish workflow then type-checks, tests, builds, checks the bundle-size budget, installs the packed tarball into a clean project to confirm both entry points work, publishes to npm with provenance, and pushes a v<version> tag.

A commit that does not change the version is not an error — the workflow sees the version already on npm and skips the release.

License

MIT © Ahmet ilhan