Show error message when JS code fails to load

Author: Turbo87

app/app.js

@@ -7,6 +7,8 @@ import config from './config/environment';
 import * as Sentry from './sentry';
 
 if (typeof FastBoot === 'undefined') {
+  // eslint-disable-next-line unicorn/prefer-add-event-listener
+  window.onerror = undefined;
   Sentry.init();
 }
 

app/index.html

@@ -28,6 +28,7 @@
 
     {{content-for 'body'}}
 
+    <script>window.onerror=function(){document.body.innerHTML='<p style="width: 70%;background: var(--main-bg);padding: 10px;">Sorry, it looks like we were not able to load the page. Please make sure your network connection works and you are using an up-to-date browser. If the issue persists, please visit our <a href="https://github.com/rust-lang/crates.io/issues/new/choose">issue tracker</a> to report the problem.</p>'}</script>
     <script src="{{rootURL}}assets/vendor.js"></script>
     <script src="{{rootURL}}assets/cargo.js"></script>