initial commit

src/features/app/app.slice.ts

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+import { createSlice, PayloadAction } from "@reduxjs/toolkit"
+
+const slice = createSlice({
+  name: "app",
+  initialState: {
+    error: null as null | string,
+    isLoading: true,
+    isAppInitialized: false,
+  },
+  reducers: {
+    setIsLoading: (state, action: PayloadAction<{ isLoading: boolean }>) => {
+      state.isLoading = action.payload.isLoading
+    },
+    setError: (state, action: PayloadAction<{ error: string | null }>) => {
+      state.error = action.payload.error
+    },
+    setIsAppInitialized: (
+      state,
+      action: PayloadAction<{ isInitialized: boolean }>,
+    ) => {
+      state.isAppInitialized = action.payload.isInitialized
+    },
+  },
+})
+
+export const appReducer = slice.reducer
+export const appActions = slice.actions

src/features/counter/Counter.module.css

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+.row {
+  display: flex;
+  align-items: center;
+  justify-content: center;
+}
+
+.row > button {
+  margin-left: 4px;
+  margin-right: 8px;
+}
+
+.row:not(:last-child) {
+  margin-bottom: 16px;
+}
+
+.value {
+  font-size: 78px;
+  padding-left: 16px;
+  padding-right: 16px;
+  margin-top: 2px;
+  font-family: "Courier New", Courier, monospace;
+}
+
+.button {
+  appearance: none;
+  background: none;
+  font-size: 32px;
+  padding-left: 12px;
+  padding-right: 12px;
+  outline: none;
+  border: 2px solid transparent;
+  color: rgb(112, 76, 182);
+  padding-bottom: 4px;
+  cursor: pointer;
+  background-color: rgba(112, 76, 182, 0.1);
+  border-radius: 2px;
+  transition: all 0.15s;
+}
+
+.textbox {
+  font-size: 32px;
+  padding: 2px;
+  width: 64px;
+  text-align: center;
+  margin-right: 4px;
+}
+
+.button:hover,
+.button:focus {
+  border: 2px solid rgba(112, 76, 182, 0.4);
+}
+
+.button:active {
+  background-color: rgba(112, 76, 182, 0.2);
+}
+
+.asyncButton {
+  composes: button;
+  position: relative;
+}
+
+.asyncButton:after {
+  content: "";
+  background-color: rgba(112, 76, 182, 0.15);
+  display: block;
+  position: absolute;
+  width: 100%;
+  height: 100%;
+  left: 0;
+  top: 0;
+  opacity: 0;
+  transition: width 1s linear, opacity 0.5s ease 1s;
+}
+
+.asyncButton:active:after {
+  width: 0%;
+  opacity: 1;
+  transition: 0s;
+}

src/features/counter/Counter.tsx

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+import { useState } from "react"
+
+import { useAppSelector, useAppDispatch } from "@/app/hooks"
+import {
+  decrement,
+  increment,
+  incrementByAmount,
+  incrementAsync,
+  incrementIfOdd,
+  selectCount,
+} from "./counterSlice"
+import styles from "./Counter.module.css"
+
+export function Counter() {
+  const count = useAppSelector(selectCount)
+  const dispatch = useAppDispatch()
+  const [incrementAmount, setIncrementAmount] = useState("2")
+
+  const incrementValue = Number(incrementAmount) || 0
+
+  return (
+    <div>
+      <div className={styles.row}>
+        <button
+          className={styles.button}
+          aria-label="Decrement value"
+          onClick={() => dispatch(decrement())}
+        >
+          -
+        </button>
+        <span className={styles.value}>{count}</span>
+        <button
+          className={styles.button}
+          aria-label="Increment value"
+          onClick={() => dispatch(increment())}
+        >
+          +
+        </button>
+      </div>
+      <div className={styles.row}>
+        <input
+          className={styles.textbox}
+          aria-label="Set increment amount"
+          value={incrementAmount}
+          onChange={(e) => setIncrementAmount(e.target.value)}
+        />
+        <button
+          className={styles.button}
+          onClick={() => dispatch(incrementByAmount(incrementValue))}
+        >
+          Add Amount
+        </button>
+        <button
+          className={styles.asyncButton}
+          onClick={() => dispatch(incrementAsync(incrementValue))}
+        >
+          Add Async
+        </button>
+        <button
+          className={styles.button}
+          onClick={() => dispatch(incrementIfOdd(incrementValue))}
+        >
+          Add If Odd
+        </button>
+      </div>
+    </div>
+  )
+}

src/features/counter/counterAPI.ts

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+// A mock function to mimic making an async request for data
+export function fetchCount(amount = 1) {
+  return new Promise<{ data: number }>((resolve) =>
+    setTimeout(() => resolve({ data: amount }), 500),
+  )
+}

src/features/counter/counterSlice.spec.ts

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+import counterReducer, {
+  CounterState,
+  increment,
+  decrement,
+  incrementByAmount,
+} from "./counterSlice"
+
+describe("counter reducer", () => {
+  const initialState: CounterState = {
+    value: 3,
+    status: "idle",
+  }
+  it("should handle initial state", () => {
+    expect(counterReducer(undefined, { type: "unknown" })).toEqual({
+      value: 0,
+      status: "idle",
+    })
+  })
+
+  it("should handle increment", () => {
+    const actual = counterReducer(initialState, increment())
+    expect(actual.value).toEqual(4)
+  })
+
+  it("should handle decrement", () => {
+    const actual = counterReducer(initialState, decrement())
+    expect(actual.value).toEqual(2)
+  })
+
+  it("should handle incrementByAmount", () => {
+    const actual = counterReducer(initialState, incrementByAmount(2))
+    expect(actual.value).toEqual(5)
+  })
+})

src/features/counter/counterSlice.ts

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+import { createAsyncThunk, createSlice, PayloadAction } from "@reduxjs/toolkit"
+import { RootState, AppThunk } from "../../app/store"
+import { fetchCount } from "./counterAPI"
+
+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 fetchCount(amount)
+    // The value we return becomes the `fulfilled` action payload
+    return response.data
+  },
+)
+
+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
+      })
+      .addCase(incrementAsync.rejected, (state) => {
+        state.status = "failed"
+      })
+  },
+})
+
+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