BLE connection from my windows pc to the bangle js 2

If you send binary data to Bangle.js over the UART connection, you can just read that out with Bluetooth.on('data', function(d) { too.

The event returns a string, but it's easy enough to use E.toUint8Array: http://www.espruino.com/Reference#l_E_toUint8Array

Bluetooth.on('data', function(d) { 
  const view = new DataView(E.toUint8Array(d).buffer);
  ... view.getInt16(0)
});