reducerFactory.ts

function reducerFactory(reducers) {
  return function combination(state, action) {
    const nextState: any = {};
    const reducerKeys = Object.keys(reducers);
    for (let i = 0; i < reducerKeys.length; i++) {
      const key = reducerKeys[i];
      const reducer: any = reducers[key];
      nextState[key] = reducer(state[key], action);
    }
    return nextState;
  }
}