Move app to separate file

src/components/app.js

@@ -0,0 +1,10 @@
+import React from 'react';
+
+export default function app() {
+    return (
+        <div>
+            <h1>JSX</h1>
+            <span>My first JSX span!</span>
+        </div>
+    );
+}

src/index.js

@@ -1,12 +1,6 @@
 import React from 'react';
 import ReactDOM from 'react-dom';
+import App from './components/app';
 
 const container = document.getElementById('container');
-const app = (
-    <div>
-        <h1>JSX</h1>
-        <span>My first JSX span!</span>
-    </div>
-);
-
-ReactDOM.render(app, container);
+ReactDOM.render(<App></App>, container);