Redux.js - простые примеры устройства.

// Устройство функции createStore() 

const defaultState = {
    counter: 0
};

function createUpAction (value) {
    return {
        type: 'UP',
        value: value
    };
}

function counterReducer (state = defaultState, action) {
  const stateCopy = lodash.cloneDeep(state);
  switch (action.type) {
    case 'UP':
      stateCopy.counter += action.value;
      return stateCopy;
    case 'DOWN':
      stateCopy.counter -= action.value
      return stateCopy;
    default:
      return state;
  }
}

const store = createStore(counterReducer);

store.dispatch(createUpAction(1));
store.getState(); // {counter: 1}

function createStore (reducer, initialState) {
    let state = initialState;
    return {
        dispatch: (action) => {state = reducer(state, action);},
        getState: () => {return state;}
    }
}


Устройство функции combineReducers()

const reducer = combineReducers({
  todoState: todoReducer,
  counterState: counterReducer
})

function counterReducer (state, action) {
  if (action.type === 'ADD') {
        return state + 1;
  } else {
        return state;
  }
}

const initialState = {
    todoState: [],
    counterState: 0,
}

const store = createStore(reducer, initialState);

function combineReducers (reducersMap) {
    return function combinationReducer (state, action) {
        const nextState = {};
        Object.entries(reducersMap).forEach(([key, reducer]) => {
              nextState[key] = reducer(state[key], action);
        });
        return nextState;
    }
}



Устройство функции applyMiddleware()

const createStoreWithMiddleware = applyMiddleware(someMiddleware)(createStore);

const store = createStoreWithMiddleware(reducer, initialState);

const thunk = (store) => (dispatch) => (action) => {
  if (typeof action === 'function') {
        return action(store.dispatch, store.getState);
  }
  return dispatch(action);
}

function createStore (reducer, initialState) {
    let state = initialState;
    return {
        dispatch: (action) => {state = reducer(state, action);},
        getState: () => {return state;}
    }
}

function applyMiddleware (middleware) {
  return function createStoreWithMiddleware (createStore) {
    return (reducer, state) => {
      const store = createStore(reducer, state);

      return {
        dispatch: action => middleware(store)(store.dispatch)(action),
        getState: store.getState
      }
    }
  }
}