Implementing Memoization in Typescript

memoize.ts

const memoize = <TS extends any[], R>(
  fn: (...args: TS) => R,
  keyfn: (...args: TS) => string = (...args: TS) => args.map((x, i) => `${i}=${x}`).join("|")
): ((...args: TS) => R) => {
  const cache: Record<string, R> = {};
  return (...args: TS) => {
    const key = keyfn(...args);
    return key in cache ? cache[key] : (cache[key] = fn(...args));
  };
};