solution

src/App.tsx

@@ -1,7 +1,57 @@
 import React from 'react';
 
-export const App: React.FC = () => (
-  <div className="App">
-    <p className="App__message">The last pressed key is [Enter]</p>
-  </div>
-);
+// class component
+
+export class App extends React.Component {
+  state = {
+    pressedKey: 'Nothing was pressed yet',
+  };
+
+  componentDidMount(): void {
+    document.addEventListener('keyup', this.handleKeyUp);
+  }
+
+  componentWillUnmount(): void {
+    document.removeEventListener('keyup', this.handleKeyUp);
+  }
+
+  handleKeyUp = (event: KeyboardEvent) => {
+    this.setState(({ pressedKey: `The last pressed key is [${event.key}]` }));
+  };
+
+  render() {
+    return (
+      <div className="App">
+        <p className="App__message">{this.state.pressedKey}</p>
+      </div>
+    );
+  }
+}
+
+// functional component
+
+// export const App: React.FC = () => {
+//   const [char, setChar] = React.useState('');
+//   const isFirstRender = React.useRef(true);
+
+//   if (char) {
+//     isFirstRender.current = false;
+//   }
+
+//   const handleKeyUp = (event: KeyboardEvent) => setChar(event.key);
+
+//   document.addEventListener('keyup', handleKeyUp);
+
+//   return (
+//     <div className="App">
+//       {!isFirstRender.current
+//         ? (
+//           <p className="App__message">
+//             {`The last pressed key is [${char}]`}
+//           </p>
+//         ) : (
+//           <p className="App__message">Nothing was pressed yet</p>
+//         )}
+//     </div>
+//   );
+// };