Can you please provide more details? Web worker means web view?
About Emulator: You should think of the Emulate tab as a Cordova API simulator, not as a device emulator. It provides you with a convenient viewport to help you visualize the approximate layout of your app on various devices and itsimulates the core Cordova APIs to make it easier to debug apps that use those APIs. It does not simulate real devices nor does it simulate third-party Cordova plugin APIs. Getting your app to work in the Emulate tab is not a guarantee that it will work on a real device. Conversely, if things work on a real device but do not work in the Emulate tab, that is not an indication that your app is "broken." The only way to know with certainty that your app works as intended is to build it and install it on real devices.
What version of iOS are you testing your application on? I recommend using services like CanIUse to determine whether a HTML5 feature is supported in the platform's specific web browser/run-time.