CODEWITHSUNDEEP
angulartypescriptngrx
AngularDebutant
AngularDebutant

Reputation: 1576

Reducer ngrx undefined initialState

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?

Upvotes: 1

Views: 1527

Answers (2)

timdeschryver
timdeschryver

Reputation: 15487

The first time that the reducers get invoked it's with an undefined state. This is done, so you're able to provide a default value for the state.

Upvotes: 1

AliF50
AliF50

Reputation: 18809

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.

Upvotes: 0

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