A memoize function written in typescript.

memoize.ts

function memoize<
  Response,
  ProvidedFunctionType extends (...args: any[]) => Response
>(
  computeExpensiveValue: ProvidedFunctionType,
  keyFunction: (...args: any[]) => string,
  cachingFunction?: () => Map<string, Response>
): ProvidedFunctionType {
  // if no caching object is provided, instanciate a Map instead.
  const hashMap = cachingFunction ? cachingFunction() : new Map();

  const memoizedFunction = (...args: any[]) => {
    const hashKey = keyFunction(...args);

    if (hashMap.has(hashKey)) {
      return hashMap.get(args.toString());
    } else {
      const response = computeExpensiveValue(...args);
      hashMap.set(hashKey, response);
      return response;
    }
  };

  return memoizedFunction as ProvidedFunctionType;
}