サンプルアプリケーションを作成

Author: mokajima

src/App.js

@@ -1,25 +1,60 @@
-import logo from './logo.svg';
-import './App.css';
+import { useState } from 'react';
+
+const App = () => {
+  console.log('renders <App />');
+
+  const [item, setItem] = useState('');
+  const [cartItems, setCartItems] = useState([]);
+
+  const handleChange = (event) => {
+    setItem(event.target.value);
+  };
+
+  const handleAdd = () => {
+    if (cartItems.includes(item)) {
+      return;
+    }
+
+    setCartItems((items) => [...items, item]);
+    setItem('');
+  };
 
-function App() {
   return (
-    <div className="App">
-      <header className="App-header">
-        <img src={logo} className="App-logo" alt="logo" />
-        <p>
-          Edit <code>src/App.js</code> and save to reload.
-        </p>
-        <a
-          className="App-link"
-          href="https://reactjs.org"
-          target="_blank"
-          rel="noopener noreferrer"
-        >
-          Learn React
-        </a>
-      </header>
+    <div style={{ margin: '10px' }}>
+      <h1>商品を購入</h1>
+      <Input value={item} onChange={handleChange} />
+      <AddButton disabled={item.trim() === ''} onClick={handleAdd} />
+      <ul>
+        {cartItems.map((item) => (
+          <li>{item}</li>
+        ))}
+      </ul>
     </div>
   );
-}
+};
+
+const Input = ({ value, onChange }) => {
+  console.log('renders <Input />');
+
+  return (
+    <p>
+      <label>
+        アイテム名: <input type="text" value={value} onChange={onChange} />
+      </label>
+    </p>
+  );
+};
+
+const AddButton = ({ disabled, onClick }) => {
+  console.log('renders <AddButton />');
+
+  return (
+    <p>
+      <button disabled={disabled} onClick={onClick}>
+        カートに追加する
+      </button>
+    </p>
+  );
+};
 
 export default App;

src/index.js

@@ -2,16 +2,10 @@ import React from 'react';
 import ReactDOM from 'react-dom';
 import './index.css';
 import App from './App';
-import reportWebVitals from './reportWebVitals';
 
 ReactDOM.render(
   <React.StrictMode>
     <App />
   </React.StrictMode>,
   document.getElementById('root')
 );
-
-// If you want to start measuring performance in your app, pass a function
-// to log results (for example: reportWebVitals(console.log))
-// or send to an analytics endpoint. Learn more: https://bit.ly/CRA-vitals
-reportWebVitals();