Redux in a nutshell

mini-redux.js

function createStore (reducers) {
  var state = reducers()
  const store = {
    dispatch: (action) => {
      state = reducers(state, action) 
    },
    getState: () => {
      return state
    } 
  }
  return store
}

const reducers = (state = { counter: 0 }, action) => {
  if (!action) { return state }
  switch (action.type) {
    case 'INCREMENT':
      return { counter: state.counter + 1  }
    case 'DECREMENT':
      return { counter: state.counter - 1  }
    default:
      return state
  }
}

const store = createStore(reducers)

store.getState() // => { counter: 0 }
store.dispatch({ type: 'INCREMENT' })
store.getState() // => { counter: 1 }