Creating a store

import { createStore } from 'redux'

// Reducer
function counter (state = { value: 0 }, action) {
  switch (action.type) {
  case 'INCREMENT':
    return { value: state.value + 1 }
  case 'DECREMENT':
    return { value: state.value - 1 }
  default:
    return state
  }
}

let store = createStore(counter)

// Optional - you can pass `initialState` as a second arg
let store = createStore(counter, { value: 0 })

A store is made from a reducer function, which takes the current state, and returns a new state depending on the action it was given.

Using a store

let store = createStore(counter)

// Dispatches an action; this changes the state
store.dispatch({ type: 'INCREMENT' })
store.dispatch({ type: 'DECREMENT' })

// Gets the current state
store.getState()

// Listens for changes
store.subscribe(() => { ... })

Dispatch actions to change the store’s state.

React Redux

Provider

import { Provider } from 'react-redux'

React.render(
  <Provider store={store}>
    <App />
  </Provider>, mountNode)

The <Provider> component makes the store available in your React components. You need this so you can use connect().

Mapping state

import { connect } from 'react-redux'

// A functional React component
function App ({ message, onMessageClick }) {
  return (
    <div onClick={() => onMessageClick('hello')}>
      {message}
    </div>
  )
}

// Maps `state` to `props`:
// These will be added as props to the component.
function mapState (state) {
  return { message: state.message }
}

// Maps `dispatch` to `props`:
function mapDispatch (dispatch) {
  return {
    onMessageClick (message) {
      dispatch({ type: 'click', message })
    }
  }
}

// Connect them:
export default connect(mapState, mapDispatch)(App)

Shorthand

export default connect(
  (state) => ({
    message: state.message
  }),
  (dispatch) => ({
    onMessageClick: (message) => {
      dispatch({ type: 'click', message })
    }
  })
)(App)

Same as above, but shorter.

Combining reducers

const reducer = combineReducers({
  counter, user, store
})

Combines multiple reducers into one reducer function. See: combineReducers (redux.js.org)

Middleware

Signature

// noop middleware
const logger = store => dispatch => action { dispatch(action) }

const logger = store => {
  // This function runs on createStore().
  // It returns a decorator for dispatch().

  return dispatch => {
    // Runs on createStore(), too.
    // It returns a new dispatch() function

    return action => {
      // Runs on every dispatch()
    }
  }
}

Middlewares are simply decorators for dispatch() to allow you to take different kinds of actions, and to perform different tasks when receiving actions.

Applying middleware

const enhancer = applyMiddleware(logger, thunk, ...)

const store = createStore(reducer, {}, enhancer)

References