init

src/App.css

@@ -1,38 +1,38 @@
 .App {
-  text-align: center;
+    text-align: center;
 }
 
 .App-logo {
-  height: 40vmin;
-  pointer-events: none;
+    height: 40vmin;
+    pointer-events: none;
 }
 
 @media (prefers-reduced-motion: no-preference) {
-  .App-logo {
-    animation: App-logo-spin infinite 20s linear;
-  }
+    .App-logo {
+        animation: App-logo-spin infinite 20s linear;
+    }
 }
 
 .App-header {
-  background-color: #282c34;
-  min-height: 100vh;
-  display: flex;
-  flex-direction: column;
-  align-items: center;
-  justify-content: center;
-  font-size: calc(10px + 2vmin);
-  color: white;
+    background-color: #282c34;
+    min-height: 100vh;
+    display: flex;
+    flex-direction: column;
+    align-items: center;
+    justify-content: center;
+    font-size: calc(10px + 2vmin);
+    color: white;
 }
 
 .App-link {
-  color: #61dafb;
+    color: #61dafb;
 }
 
 @keyframes App-logo-spin {
-  from {
-    transform: rotate(0deg);
-  }
-  to {
-    transform: rotate(360deg);
-  }
+    from {
+        transform: rotate(0deg);
+    }
+    to {
+        transform: rotate(360deg);
+    }
 }

src/App.js

@@ -1,26 +1,42 @@
 import React from 'react';
 import logo from './logo.svg';
 import './App.css';
+import ReactDOM from "react-dom";
+import TodoApp from "./Zwei"
 
 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>
-  );
+    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>
+                <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>
+    );
 }
 
 export default App;

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.css

@@ -1,13 +1,13 @@
 body {
-  margin: 0;
-  font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', 'Roboto', 'Oxygen',
+    margin: 0;
+    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', 'Roboto', 'Oxygen',
     'Ubuntu', 'Cantarell', 'Fira Sans', 'Droid Sans', 'Helvetica Neue',
     sans-serif;
-  -webkit-font-smoothing: antialiased;
-  -moz-osx-font-smoothing: grayscale;
+    -webkit-font-smoothing: antialiased;
+    -moz-osx-font-smoothing: grayscale;
 }
 
 code {
-  font-family: source-code-pro, Menlo, Monaco, Consolas, 'Courier New',
+    font-family: source-code-pro, Menlo, Monaco, Consolas, 'Courier New',
     monospace;
 }

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();