init

src/App.js

@@ -1,6 +1,8 @@
 import React from 'react';
 import logo from './logo.svg';
 import './App.css';
+import ReactDOM from "react-dom";
+import TodoApp from "./Zwei"
 
 function App() {
     return (
@@ -18,6 +20,20 @@ function App() {
                 >
                     Learn React
                 </a>
+                <button>klick me to get to another pagexD</button>
+                <button className="square" onClick={
+                    () => {
+                        console.log("rerendering dom");
+                        ReactDOM.render(
+                            <React.StrictMode>
+                                <TodoApp />
+                            </React.StrictMode>,
+                            document.getElementById('root')
+                        );
+                    }
+                }>
+                    blabla
+                </button>
             </header>
         </div>
     );

src/App.test.js

@@ -1,9 +0,0 @@
-import React from 'react';
-import { render } from '@testing-library/react';
-import App from './App';
-
-test('renders learn react link', () => {
-  const { getByText } = render(<App />);
-  const linkElement = getByText(/learn react/i);
-  expect(linkElement).toBeInTheDocument();
-});

src/Zwei.js

@@ -0,0 +1,65 @@
+import React from 'react';
+
+class TodoApp extends React.Component {
+    constructor(props) {
+        super(props);
+        this.state = { items: [], text: '' };
+        this.handleChange = this.handleChange.bind(this);
+        this.handleSubmit = this.handleSubmit.bind(this);
+    }
+
+    render() {
+        return (
+            <div>
+                <h3>TODO</h3>
+                <TodoList items={this.state.items} />
+                <form onSubmit={this.handleSubmit}>
+                    <label htmlFor="new-todo">
+                        What needs to be done?
+                    </label>
+                    <input
+                        id="new-todo"
+                        onChange={this.handleChange}
+                        value={this.state.text}
+                    />
+                    <button>
+                        Add #{this.state.items.length + 1}
+                    </button>
+                </form>
+            </div>
+        );
+    }
+
+    handleChange(e) {
+        this.setState({ text: e.target.value });
+    }
+
+    handleSubmit(e) {
+        e.preventDefault();
+        if (this.state.text.length === 0) {
+            return;
+        }
+        const newItem = {
+            text: this.state.text,
+            id: Date.now()
+        };
+        this.setState(state => ({
+            items: state.items.concat(newItem),
+            text: ''
+        }));
+    }
+}
+
+class TodoList extends React.Component {
+    render() {
+        return (
+            <ul>
+                {this.props.items.map(item => (
+                    <li key={item.id}>{item.text}</li>
+                ))}
+            </ul>
+        );
+    }
+}
+
+export default TodoApp;

src/index.js

@@ -14,4 +14,4 @@ ReactDOM.render(
 // If you want your app to work offline and load faster, you can change
 // unregister() to register() below. Note this comes with some pitfalls.
 // Learn more about service workers: https://bit.ly/CRA-PWA
-serviceWorker.unregister();
+serviceWorker.register();