5 files changed, 257 insertions, 0 deletions
diff --git a/src/features/counter/Counter.jsx b/src/features/counter/Counter.jsx
new file mode 100644
index 0000000..37d866d
--- /dev/null
+++ b/src/features/counter/Counter.jsx
@@ -0,0 +1,67 @@
+import React, { useState } from "react";
+import { useSelector, useDispatch } from "react-redux";
+import {
+  decrement,
+  increment,
+  incrementByAmount,
+  incrementAsync,
+  incrementIfOdd,
+  selectCount,
+} from "./counterSlice";
+import styles from "./Counter.module.css";
+
+export function Counter() {
+  const count = useSelector(selectCount);
+  const dispatch = useDispatch();
+  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>
+  );
+}
diff --git a/src/features/counter/Counter.module.css b/src/features/counter/Counter.module.css
new file mode 100644
index 0000000..9e70f8e
--- /dev/null
+++ b/src/features/counter/Counter.module.css
@@ -0,0 +1,78 @@
+.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;
+}
diff --git a/src/features/counter/counterAPI.js b/src/features/counter/counterAPI.js
new file mode 100644
index 0000000..cc9b4a4
--- /dev/null
+++ b/src/features/counter/counterAPI.js
@@ -0,0 +1,6 @@
+// A mock function to mimic making an async request for data
+export function fetchCount(amount = 1) {
+  return new Promise((resolve) =>
+    setTimeout(() => resolve({ data: amount }), 500)
+  );
+}
diff --git a/src/features/counter/counterSlice.js b/src/features/counter/counterSlice.js
new file mode 100644
index 0000000..a9441ac
--- /dev/null
+++ b/src/features/counter/counterSlice.js
@@ -0,0 +1,73 @@
+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;
diff --git a/src/features/counter/counterSlice.spec.js b/src/features/counter/counterSlice.spec.js
new file mode 100644
index 0000000..113526b
--- /dev/null
+++ b/src/features/counter/counterSlice.spec.js
@@ -0,0 +1,33 @@
+import counterReducer, {
+  increment,
+  decrement,
+  incrementByAmount,
+} from "./counterSlice";
+
+describe("counter reducer", () => {
+  const initialState = {
+    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);
+  });
+});