Answering the question of "Is my bluetooth on?" in React Native

This module only works for iOS at the moment.

$ npm install react-native-bluetooth-state

React Native >=0.7.0 is needed.

You then need to add the Objective-C part to your XCode project. Drag RNBluetoothState.xcodeproj from the node_modules/react-native-bluetooth-state folder into your XCode project. Click on the your project in XCode, goto Build Phases then Link Binary With Libraries and add libRNBluetoothState.a and CoreBluetooth.framework.

(Alternatively you can use RNPM to link the library, but in any case you need to link against CoreBluetooth.framework.)

import BluetoothState from 'react-native-bluetooth-state';

BluetoothState.subscribe(bluetoothState => {
  // bluetoothState can either be "on", "off", "unknown", "unauthorized", "resetting" or "unsupported‚"
});

// Initialize needs to be called otherwise we don't get the initial state
BluetoothState.initialize();

Unlicense or MIT. Whatever fits your purpose best.