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

as per the documentation of redux: https://redux.js.org/basics/reducers

you need to return state out side of switch function like this:

 function posts(state=initialState,action) {
  switch (action.type) {
    case INVALIDATE_SUBREDDIT:
      return state.merge({
        didInvalidate: true
      })
    case REQUEST_POSTS:
      return state.merge({
        isFetching: true,
        didInvalidate: false
      })
    case RECEIVE_POSTS:
      return state.merge({
        isFetching: false,
        didInvalidate: false,
        items: action.posts,
        lastUpdated: action.receivedAt
      })
    default:
      return state 
    }

//here you should put the return state
return state
}