Code of ESP8266 for Serial communication between ESP8266 and Arduino

Serial_communication_of_ESP8266.ino

#include<SoftwareSerial.h> //Included SoftwareSerial Library
//Started SoftwareSerial at RX and TX pin of ESP8266/NodeMCU
SoftwareSerial s(3,1);

void setup() {
  //Serial S Begin at 9600 Baud
  s.begin(9600);
}

void loop() {
  //Write '123' to Serial
  s.write(123);
  delay(1000);
}