Typescript memoize decorator

memoaize.decorator.ts

const MEMOIZED_VALUE_KEY = '_memoizedValue';

export function memoize(expirationTimeMs: number = 60000) {
  return (target: any, propertyName: string, descriptor: TypedPropertyDescriptor<any>) => {
    if (descriptor.value != null) {
      const originalMethod = descriptor.value;
      const fn: any = function (...args: any[]) {
        const key = MEMOIZED_VALUE_KEY + '_' + JSON.stringify(args);

        if (!fn[key]) {
          fn[key] = originalMethod.apply(this, args);
          setTimeout(() => clearMemoizedValue(fn, key), expirationTimeMs);
        }

        return fn[key];
      };
      descriptor.value = fn;

      return descriptor;
    } else {
      throw Error('Only put the @memoize decorator on a method.');
    }
  };
}

export function clearMemoizedValue(method: any, key: string) {
  delete method[key];
}