Added memo()

package.json

@@ -66,7 +66,7 @@
     "url": "https://github.com/webdeveric/utils/issues"
   },
   "homepage": "https://github.com/webdeveric/utils/#readme",
-  "packageManager": "pnpm@10.30.3+sha512.c961d1e0a2d8e354ecaa5166b822516668b7f44cb5bd95122d590dd81922f606f5473b6d23ec4a5be05e7fcd18e8488d47d978bbe981872f1145d06e9a740017",
+  "packageManager": "pnpm@10.31.0+sha512.e3927388bfaa8078ceb79b748ffc1e8274e84d75163e67bc22e06c0d3aed43dd153151cbf11d7f8301ff4acb98c68bdc5cadf6989532801ffafe3b3e4a63c268",
   "scripts": {
     "clean": "rimraf ./dist/",
     "prebuild": "pnpm clean",
@@ -87,7 +87,7 @@
   "devDependencies": {
     "@commitlint/config-conventional": "^20.4.3",
     "@commitlint/types": "^20.4.3",
-    "@types/node": "^24.11.0",
+    "@types/node": "^24.12.0",
     "@vitest/coverage-v8": "^4.0.18",
     "@webdeveric/eslint-config-ts": "^0.12.0",
     "@webdeveric/prettier-config": "^0.3.0",

src/memo.ts

@@ -0,0 +1,48 @@
+import type { AnyFunction } from './types/common.js';
+
+export type CacheKeyFn<Fn extends AnyFunction, ReturnValue = unknown> = (args: Parameters<Fn>) => ReturnValue;
+
+export type DefaultCacheKeyFn<Fn extends AnyFunction> = CacheKeyFn<Fn, NonNullable<Parameters<Fn>[0]> | string>;
+
+export type MemoizedFn<Fn extends AnyFunction, CkFn extends CacheKeyFn<Fn>> = Fn & {
+  cache: Map<ReturnType<CkFn>, ReturnType<Fn>>;
+};
+
+/**
+ * Memoize a function
+ *
+ * @todo use `Map.getOrInsertComputed()` once it is widely available.
+ */
+export function memo<Fn extends AnyFunction, CkFn extends CacheKeyFn<Fn>>(
+  fn: Fn,
+  getCacheKey: CkFn,
+): MemoizedFn<Fn, CkFn>;
+
+export function memo<Fn extends AnyFunction>(fn: Fn): MemoizedFn<Fn, DefaultCacheKeyFn<Fn>>;
+
+export function memo<Fn extends AnyFunction, CkFn extends CacheKeyFn<Fn>>(
+  fn: Fn,
+  getCacheKey?: CkFn,
+): MemoizedFn<Fn, CkFn> {
+  const defaultGetCacheKey: DefaultCacheKeyFn<Fn> = (args) => args[0] ?? JSON.stringify(args);
+
+  const resolvedGetCacheKey = getCacheKey ?? defaultGetCacheKey;
+
+  const memoized = (...args: Parameters<Fn>): ReturnType<Fn> => {
+    const key = resolvedGetCacheKey(args);
+
+    if (memoized.cache.has(key)) {
+      return memoized.cache.get(key);
+    }
+
+    const value = fn(...args);
+
+    memoized.cache.set(key, value);
+
+    return value;
+  };
+
+  memoized.cache = new Map();
+
+  return memoized as MemoizedFn<Fn, CkFn>;
+}