public class MainActivity extends ReactActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        WritableMap map = Arguments.createMap();
        map.putString("key1", "Value1");
   map.putString("key1", "Value1");

        try {
          getReactInstanceManager().getCurrentReactContext()
            .getJSModule(DeviceEventManagerModule.RCTDeviceEventEmitter.class)
            .emit("customEventName", map);
        } catch (Exception e){
          Log.e("ReactNative", "Caught Exception: " + e.getMessage());
        }
    }

import { DeviceEventEmitter } from 'react-native';

componentWillMount: function() {
  DeviceEventEmitter.addListener('keyboardWillShow', function(e: Event) {
    // handle event.
  });