Why do I get “Reducer […] returned undefined during initialization” despite providing initialState to createStore()?

Question

I had set InitialState in my redux createStore method ,and I corresponding InitialState as second arguments

I got a error in browser:

Un         


        

Answer 1

I just hit this same snag because I accidentally redefined state inside my reducer:

const initialState = {
  previous: true,
  later: true
}

const useTypeReducer = (state = initialState, action) => {
  switch (action.type) {
    case 'TOGGLE_USE_TYPES':
      let state = Object.assign({}, state);   // DON'T REDEFINE STATE LIKE THIS!
      state[action.use] = !state[action.use];
      return state;

    default:
      return state;
  }
}

export default useTypeReducer;

To fix the problem I needed to refrain from redefining state:

const initialState = {
  previous: true,
  later: true
}

const useTypeReducer = (state = initialState, action) => {
  switch (action.type) {
    case 'TOGGLE_USE_TYPES':
      let _state = Object.assign({}, state);   // BETTER
      _state[action.use] = !state[action.use];
      return _state;

    default:
      return state;
  }
}

export default useTypeReducer;