cra-template-jam/template/src/features/counter/counterSlice.ts

A quick start Create React App template with React Router, Redux Toolkit, TypeScript, Styled Components and custom ESlint configurations

import { createAsyncThunk, createSlice, PayloadAction } from '@reduxjs/toolkit';
import { RootState, AppThunk } from '../../app/store';

export interface CounterState {
  value: number;
  status: 'idle' | 'loading' | 'failed';
}

const initialState: CounterState = {
    value: 0,
    status: 'idle',
};

// The function below is called a thunk and allows us to perform async logic. It
// can be dispatched like a regular action: `dispatch(incrementAsync(10))`. This
// will call the thunk with the `dispatch` function as the first argument. Async
// code can then be executed and other actions can be dispatched. Thunks are
// typically used to make async requests.
export const incrementAsync = createAsyncThunk(
    'counter/fetchCount',
    async (amount: number) => {
        const response = await new Promise<number>((resolve, reject) => setTimeout(() => resolve(amount), 500));
        // The value we return becomes the `fulfilled` action payload

        return response;
    },
);

export const counterSlice = createSlice({
    name: 'counter',
    initialState,
    // The `reducers` field lets us define reducers and generate associated actions
    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;
        },
        // Use the PayloadAction type to declare the contents of `action.payload`
        incrementByAmount: (state, action: PayloadAction<number>) => {
            state.value += action.payload;
        },
    },
    // The `extraReducers` field lets the slice handle actions defined elsewhere,
    // including actions generated by createAsyncThunk or in other slices.
    extraReducers: builder => {
        builder
            .addCase(incrementAsync.pending, state => {
                state.status = 'loading';
            })
            .addCase(incrementAsync.fulfilled, (state, action) => {
                state.status = 'idle';
                state.value += action.payload;
            });
    },
});

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

// The function below is called a selector and allows us to select a value from
// the state. Selectors can also be defined inline where they're used instead of
// in the slice file. For example: `useSelector((state: RootState) => state.counter.value)`
export const selectCount = (state: RootState) => state.counter.value;

// We can also write thunks by hand, which may contain both sync and async logic.
// Here's an example of conditionally dispatching actions based on current state.
export const incrementIfOdd = (amount: number): AppThunk => (
    dispatch,
    getState,
) => {
    const currentValue = selectCount(getState());

    if (currentValue % 2 === 1) {
        dispatch(incrementByAmount(amount));
    }
};

export default counterSlice.reducer;