Argument of type 'any' is not assignable to parameter of type 'never' - Array passed

Question

I'm learning TypeScript, and when I try to set a reducer in redux Toolkit like this :

const testSlice = createSlice({
  name: "test",
  initialState: [],
  reducers: {
    callApi: (state, action) => {
      const getData = {
        type: "test/getData",
        data: action.payload
      };

      state.push(getData);
    }
  }
});

I get state.push(getData) underlined in red in VSCode, and the error : Argument of type 'any' is not assignable to parameter of type 'never'

I tried to write : const getData : any[] = { but still have the same error.

Can someone tell me where is my mistake ?

Thank you !

Answer 1

This is happening because you assign empty array to initialState without specifying its type. TS then inferring type as never[]

type TestState = any[];

const initialState: TestState = [];

const testSlice = createSlice({
  name: "test",
  initialState,
  reducers: {
    callApi: (state, action) => {
      const getData = {
        type: "test/getData",
        data: action.payload
      };

      state.push(getData);
    }
  }
});

This should solve a problem, however I would recommend not using any type