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diff --git a/src/features/counter/counterSlice.js b/src/features/counter/counterSlice.js
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+import { createAsyncThunk, createSlice } from "@reduxjs/toolkit";
+import { fetchCount } from "./counterAPI";
+
+const initialState = {
+  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) => {
+    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) => {
+      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) => 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) => (dispatch, getState) => {
+  const currentValue = selectCount(getState());
+  if (currentValue % 2 === 1) {
+    dispatch(incrementByAmount(amount));
+  }
+};
+
+export default counterSlice.reducer;