Merge branch 'feature/flow-typed/appjs-patch'

1 files changed, 12 insertions, 4 deletions

diff --git a/app/app.js b/app/app.js
index 1ef9bc7e14..c3d5acbcb8 100644
--- a/app/app.js
+++ b/app/app.js
@@ -75,12 +75,10 @@ backend.on('disconnect', updateTrayIcon);
 // force update tray
 updateTrayIcon();
 
-const rootElement = document.querySelector(document.currentScript.getAttribute('data-container'));
-
 // disable smart pinch.
 webFrame.setZoomLevelLimits(1, 1);
 
-if ('serviceWorker' in navigator) {
+if(navigator.serviceWorker) {
   navigator.serviceWorker.register(path.join(__dirname, 'tilecache.sw.js'))
     .then((registration) => {
       log.info('ServiceWorker registration successful with scope: ', registration.scope);
@@ -91,6 +89,16 @@ if ('serviceWorker' in navigator) {
 
 ipcRenderer.send('on-browser-window-ready');
 
+const containerId = document.currentScript.getAttribute('data-container');
+if(!containerId) {
+  throw new Error('Missing data-container attribute.');
+}
+
+const rootElement = document.querySelector(containerId);
+if(!rootElement) {
+  throw new Error('Missing root element.');
+}
+
 ReactDOM.render(
   <Provider store={ store }>
     <ConnectedRouter history={ memoryHistory }>
@@ -98,4 +106,4 @@ ReactDOM.render(
     </ConnectedRouter>
   </Provider>,
   rootElement
-);
+);
\ No newline at end of file