Reducer ngrx undefined initialState

Question

I am updating to ngrx 8, and I noticed that in the reducer function the type of the state parameter can be either State or undefined

https://ngrx.io/guide/store/reducers#creating-the-reducer-function

export function reducer(state: State | undefined, action: Action) {
  return scoreboardReducer(state, action);
}

Is there any reason for the undefined optional type?

Answer 1

My opinion is that it is for type checking for default parameters. To set the initialState, you can do

export function reducer(state: State | undefined = {}, action: Action) {
  return scoreboardReducer(state, action);
}

Check out the = {}. If state is undefined, it will be equal to {}.

You can set the initialState when undefined or just leave it.