Stateless reducers

[yhnavein]

Hi,

I noticed in this repository reducers being written in this way:

reducers: {
    getRepoDetailsSuccess(state, action: PayloadAction<RepoDetails>) {
      state.openIssuesCount = action.payload.open_issues_count
      state.error = null
    },
}

Isn't it wrong? It looks like the reducer is changing an existing state, which must not happen.

IMHO reducers should look like

reducers: {
    getRepoDetailsSuccess(state, action: PayloadAction<RepoDetails>) {
      return {
        ...state,
        openIssuesCount: action.payload.open_issues_count,
        error: null
      };
    },
}

Am I missing something?

[markerikson]

Yes. As discussed in the tutorials and documentation, Redux Toolkit uses Immer inside, which allows you to write "mutating" code that is actually turned into correct immutable updates inside:

https://redux-toolkit.js.org/tutorials/intermediate-tutorial#mutable-update-logic

https://redux-toolkit.js.org/usage/usage-guide#simplifying-reducers-with-createreducer

https://redux.js.org/recipes/structuring-reducers/immutable-update-patterns#immutable-update-utility-libraries