ES6 initial setup

src/demo/index.js

@@ -0,0 +1,15 @@
+import App from './App';
+
+/**
+ * Initializing demo
+ */
+new App();
+
+/**
+ * Adding preview (demo only)
+ */
+document.querySelector('.simple-keyboard').insertAdjacentHTML('beforebegin', `
+  <div class="simple-keyboard-preview">
+    <textarea class="input" readonly>Hello World!</textarea>
+  </div>
+`);