group action and function result

group action function.js

//group promise returning function
const createGroup = (cache) => (
  fn,
  getKey = (...x) => JSON.stringify(x)
) => (...args) => {
  const key = getKey(args);
  let result = cache.get(key);
  if (result) {
    return result;
  }
  //no cache
  result = Promise.resolve(fn.apply(null, args)).then(
    (r) => {
      cache.resolved(key); //tell cache promise is done
      return r;
    },
    (e) => {
      cache.resolve(key); //tell cache promise is done
      return Promise.reject(e);
    }
  );
  cache.set(key, result);
  return result;
};
//thunk action creators are not (...args)=>result but
//  (...args)=>(dispatch,getState)=>result
//  so here is how we group thunk actions
const createGroupedThunkAction = (thunkAction, cache) => {
  const group = createGroup(
    cache
  )((args, dispatch, getState) =>
    thunkAction.apply(null, args)(dispatch, getState)
  );

  return (...args) => (dispatch, getState) => {
    return group(args, dispatch, getState);
  };
};
//permanent memory cache store creator
const createPermanentMemoryCache = (cache = new Map()) => {
  return {
    get: (key) => cache.get(key),
    set: (key, value) => cache.set(key, value),
    resolved: (x) => x,
  };
};