This code is for DOIT Motor Shield which has L293D motor driver and takes a NODEMCU ESP8266 board. With this you can convert BYJ48 stepper motor from Unipolar to Bipolar

BYJ48-Bipolar

int A = D1; //EN1
int B = D2; //EN2
int C = D3; //IN1
int D = D4; //IN3
long del = 2000;

void setup() {                
  pinMode(A, OUTPUT);   
  pinMode(B, OUTPUT);     
  pinMode(C, OUTPUT);   
  pinMode(D, OUTPUT);    
  digitalWrite(A, HIGH);    
  digitalWrite(B, HIGH);    
}

void one(){
  digitalWrite(C, LOW);   
  digitalWrite(D, HIGH);   
  delayMicroseconds(del);
}
void two(){
  digitalWrite(C, LOW);    
  digitalWrite(D, LOW);    
  delayMicroseconds(del);
}
void three(){
  digitalWrite(C, HIGH);  
  digitalWrite(D, LOW);    
  delayMicroseconds(del);
}
void four(){
  digitalWrite(C, HIGH);   
  digitalWrite(D, HIGH);   
  delayMicroseconds(del);
}
// the loop routine runs over and over again forever:
void loop() {

  for (int i=0; i<=500; i++){
    one(); 
    two();
    three();
    four();
  }
  
  delay(2000);
 
}