How do I add an element to array in reducer of React native redux?

Issue

How do I add elements in my array arr[] of redux state in reducer? I am doing this-

import {ADD_ITEM} from '../Actions/UserActions'
const initialUserState = {
    arr:[]
}

export default function userState(state = initialUserState, action)
{
    console.log(arr);
    switch (action.type)
    {
        case ADD_ITEM: 
            return { 
                      ...state,
                      arr: state.arr.push([action.newItem])
                   }

        default:
            return state
    }
}

Solution

Since this question gets a lot of exposure:

If you are looking for the answer to this question, there is a good chance that you are following a very outdated Redux tutorial.

The official recommendation (since 2019) is to use the official Redux Toolkit to write modern Redux code.

Among other things, that will eliminate string action constants and generate action creators for you.

It will also employ methods that allow you to just write mutating logic in your Reducers created by createReducer or createSlice, so there is no need to write immutable code in Reducers in modern Redux in the first place.

Please follow the official Redux tutorials instead of third-party tutorials to always get the most up-to-date information on good Redux practices and will also show you how to use Redux Toolkit in different common scenarios.

For comparison, in modern Redux this would look like

const userSlice = createSlice({
  name: "user",
  initialState: {
    arr:[]
  },
  reducers: {
    // no ACTION_TYPES, this will internally create a type "user/addItem" that you will never use by hand. You will only see it in the devTools
    addItem(state, action) {
      // you can use mutable logic in createSlice reducers
      state.arr.push(action.payload)
    }
  }
})

// autogenerated action creators
export const { addItem } = slice.actions;

// and export the final reducer
export default slice.reducer;

Answered By - phry