Is this a bug report?

Yes

Environment

OS:  macOS Sierra 10.13.1
Node:  8.9.1
Yarn:  0.21.3
npm:  5.5.1
Xcode:  Xcode 9.1 Build version 9B55

react-native: 0.50.3
react: 16.0.0
Test device: Simulator iPhone6s / iOS11

Steps to Reproduce

1. create a pure app with command: react-init geoTest

2. Setup the app as following: include NSLocationAlwaysUsageDescription and NSLocationWhenInUseUsageDescription in the info.plist, add location as a background mode in the 'Capabilities' tab in Xcode

3. Add code as below:

componentDidMount() {
     navigator.geolocation.getCurrentPosition(
          (position) => {
            console.log("position.coords: ", position.coords);
          },
          (error) => this.setState({ error: error.message }),
          { enableHighAccuracy: true, useSignificantChanges: true, distanceFilter:10, timeout: 20000, maximumAge: 1000 },
        );
}

Below error message show up:

TypeError: Cannot read property 'geolocation' of undefined