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:

1. Navigate to your app in the browser.
2. In the same tab go to about:debug
3. Reload (it may reload for you).
4. 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.