Note that this may or may not work on your device. If you're running into an app that works in a real browser but on in your Android's stock browser, do this:
- Navigate to your app in the browser.
- In the same tab go to
about:debug - Reload (it may reload for you).
- Profit.
This will show you errors that even window.onerror doesn't catch, which should help you narrow down your problem(s).
Source: This stackoverflow answer.