How to use module "ble_uart" and handle passkeyRequest?

I think since you pass the device into ble_uart, you could do something like:

NRF.requestDevice({ filters: [{ namePrefix: 'Puck.js' }] }).then(function(device) {
  device.on('passkeyRequest', function() { 
    device.sendPasskey("123456");
   });
  return ble_uart.connect(device);
}).then(function(uart) {
  uart.on('data', function(d) { print("Got:"+JSON.stringify(d)); });
  uart.eval('E.getTemperature()').then(function(data) {
    print("Got temperature "+data);
    uart.write("digitalPulse(LED,1,10);\n"); // .then(...)
  }); 
  setTimeout(function() { 
    uart.disconnect(); 
    console.log("Disconnected"); 
  }, 2000);
});

Not tested though