allow for customising of the hash return type as H

Author: keithamus

index.ts

@@ -1,32 +1,33 @@
-export interface MemoizeOptions<A extends unknown[], R> {
+
+export interface MemoizeOptions<A extends unknown[], R, H = unknown> {
   /**
    * Provides a single value to use as the Key for the memoization.
    * Defaults to `JSON.stringify` (ish).
    */
-  hash?: (...args: A) => unknown
+  hash?: (...args: A) => H
 
   /**
    * The Cache implementation to provide. Must be a Map or Map-alike.
    * Defaults to a Map. Useful for replacing the cache with an LRU cache or similar.
    */
-  cache?: Map<unknown, R>
+  cache?: Map<H, R>
 }
 
 export type MemoizableFunction<A extends unknown[], R extends unknown, T extends unknown> = (this: T, ...args: A) => R
 
-export function defaultHash(...args: unknown[]): string {
+export function defaultHash<A extends unknown[], H extends unknown>(...args: A): H {
   // JSON.stringify ellides `undefined` and function values by default. We do not want that.
-  return JSON.stringify(args, (_: unknown, v: unknown) => (typeof v === 'object' ? v : String(v)))
+  return JSON.stringify(args, (_: unknown, v: unknown) => (typeof v === 'object' ? v : String(v))) as H
 }
 
-export default function memoize<A extends unknown[], R extends unknown, T extends unknown>(
+export default function memoize<A extends unknown[], R extends unknown, T extends unknown, H extends unknown>(
   fn: MemoizableFunction<A, R, T>,
-  opts: MemoizeOptions<A, R> = {}
+  opts: MemoizeOptions<A, R, H> = {}
 ): MemoizableFunction<A, R, T> {
-  const {hash = defaultHash, cache = new Map()} = opts
-  return function (this: T, ...args: A) {
+  const {hash = defaultHash, cache = new Map<H, R>()} = opts
+  return function (this: T, ...args: A): R {
     const id = hash.apply(this, args)
-    if (cache.has(id)) return cache.get(id)
+    if (cache.has(id)) return cache.get(id)!
     let result = fn.apply(this, args)
     if (result instanceof Promise) {
       // eslint-disable-next-line github/no-then