I uploaded this code onto the Arduino Uno:

#include "SoftwareSerial.h"

SoftwareSerial esp8266(2, 3); // RX, TX

void setup()
{
  Serial.begin(9600); // serial port used for debugging
  esp8266.begin(9600);  // your ESP's baud rate might be different
}

void loop()
{
  if(esp8266.available())  // check if the ESP is sending a message
  {
   while(esp8266.available())
    {
      char c = esp8266.read();  // read the next character.

      Serial.write(c);  // writes data to the serial monitor
    }
  }

  if(Serial.available())
  {
    delay(10);  // wait to let all the input command in the serial buffer
    // read the input command in a string
    String cmd = "";
    while(Serial.available())
    {
      cmd += (char)Serial.read();
    }
    // send to the esp8266
    esp8266.println(cmd); 
  }
}

After that, I was able to follow through the tutorial and got this response in the Serial Monitor:

Note: The reason why I switched to mode 3 is because I want to control an Arduino Pro Mini using NodeJS. I followed another tutorial and I figured that I need to connect to an ESP8266 access point.

The nodejs code is below:

After that, I was able to follow through the tutorial and got this response in the Serial Monitor:

Note: The reason why I switched to mode 3 is because I want to control an Arduino Pro Mini (instead of Arduino Pro) using NodeJS. I followed another tutorial and I figured that I need to connect to an ESP8266 access point.

I uploaded the StandardFirmataSketchPlus to my Arduino Pro Mini, with the baud rate set to 115200 (which is the same baud rate with my ESP8266). The schematic I used is similar to the one below, except I used a 3.3V Pro Mini and a Lipo battery, instead of a 5V:

The nodejs code is below:

This code is to test the connection between Arduino and Nodejs and when I run this file, it doesn't work.

The nodejs code is below:

var VirtualSerialPort = require('udp-serial').SerialPort;
var firmata = require('firmata');
var five = require("johnny-five");
var sp = new VirtualSerialPort({
  host: '192.168.1.243' //I got this number from the AT command (STAIP above)
 });

var io = new firmata.Board(sp);

io.once('ready', function(){
    io.isReady = true;

    var board = new five.Board({io: io, repl: true});

    board.on('ready', function(){
        var led = new five.Led(12);
        led.blink(3000);
    });
});