where is counterReducer from?

[snowden-fu]

In official demo, I have noticed counterReducer is from counterSlice, but actually, there is no counterReducer in counterSlice file, so i am wondering where is counterReducer from?

import { configureStore } from '@reduxjs/toolkit'
import counterReducer from '../features/counter/counterSlice'

export default configureStore({
  reducer: {
    counter: counterReducer
  }
})

below is counterSlice.js

import { createSlice } from '@reduxjs/toolkit'

export const counterSlice = createSlice({
  name: 'counter',
  initialState: {
    value: 0
  },
  reducers: {
    increment: state => {
      // Redux Toolkit allows us to write "mutating" logic in reducers. It
      // doesn't actually mutate the state because it uses the immer library,
      // which detects changes to a "draft state" and produces a brand new
      // immutable state based off those changes
      state.value += 1
    },
    decrement: state => {
      state.value -= 1
    },
    incrementByAmount: (state, action) => {
      state.value += action.payload
    }
  }
})

export const { increment, decrement, incrementByAmount } = counterSlice.actions

export default counterSlice.reducer

[markerikson]

It's an ES module "default import/export".

When you do export default whatever, another file can do import AnyNameYouWantHere from "./some/other/file".

In this case, I called it counterReducer, but I could have called it import fred or import aldkfjalsdkflkasjdf. It's just creating a variable name in the importing file.