Write commands from react native application

You might find this handy: http://www.espruino.com/About+Bluetooth+LE#services-and-characteristics

It's the NRF.setServices function that you'll need on Puck.js, and there is some example code in http://www.espruino.com/Reference#l_NRF_setServices

For instance:

NRF.setServices({
  0xBCDE : {
    0xABCD : {
      writable : true,
      onWrite : function(evt) {
        digitalWrite([LED3,LED2,LED1], evt.data[0]);
      }
    }
  }
});

Will let you change the state of the 3 LEDs.

Your other option is to write raw JS code to the 'UART' characteristic on Puck.js - it's a bit less efficient but that way you don't have to have any specific code on the Puck...