react-hackathon-board/react-hackathon/src/redux/modules/counter.js

Hackathon board with React/node/mongo

/* @flow */
// ------------------------------------
// Constants
// ------------------------------------
export const COUNTER_INCREMENT = 'COUNTER_INCREMENT';

// ------------------------------------
// Actions
// ------------------------------------
// NOTE: "Action" is a Flow interface defined in https://github.com/TechnologyAdvice/flow-interfaces
// If you're unfamiliar with Flow, you are completely welcome to avoid annotating your code, but
// if you'd like to learn more you can check out: flowtype.org.
// DOUBLE NOTE: there is currently a bug with babel-eslint where a `space-infix-ops` error is
// incorrectly thrown when using arrow functions, hence the oddity.
export function increment (value: number = 1): Action {
  return {
    type: COUNTER_INCREMENT,
    payload: value
  };
}

// This is a thunk, meaning it is a function that immediately
// returns a function for lazy evaluation. It is incredibly useful for
// creating async actions, especially when combined with redux-thunk!
// NOTE: This is solely for demonstration purposes. In a real application,
// you'd probably want to dispatch an action of COUNTER_DOUBLE and let the
// reducer take care of this logic.
export const doubleAsync = (): Function => {
  return (dispatch: Function, getState: Function): Promise => {
    return new Promise((resolve: Function): void => {
      setTimeout(() => {
        dispatch(increment(getState().counter));
        resolve();
      }, 200);
    });
  };
};

export const actions = {
  increment,
  doubleAsync
};

// ------------------------------------
// Action Handlers
// ------------------------------------
const ACTION_HANDLERS = {
  [COUNTER_INCREMENT]: (state: number, action: {payload: number}): number => state + action.payload
};

// ------------------------------------
// Reducer
// ------------------------------------
const initialState = 0;
export default function counterReducer (state: number = initialState, action: Action): number {
  const handler = ACTION_HANDLERS[action.type];

  return handler ? handler(state, action) : state;
}