Warn user before navigating away/unloading

src/index.jsx

@@ -7,6 +7,11 @@ import ProjectLoaderHOC from './lib/project-loader-hoc.jsx';
 
 import styles from './index.css';
 
+if (process.env.NODE_ENV === 'production' && typeof window === 'object') {
+    // Warn before navigating away
+    window.onbeforeunload = () => true;
+}
+
 const App = AppStateHOC(ProjectLoaderHOC(GUI));
 
 const appTarget = document.createElement('div');