const int buttonPin = 2;
const int ledPin = 4;
const int ledPin2 = 5;
int buttonState = 0;
int lastMillis = 0;

void IRAM_ATTR function_ISR() {
 if(millis() - lastMillis > 10){ // Software debouncing buton
         ets_printf("ISR triggered\n");
         buttonState = !buttonState;
         digitalWrite(ledPin,buttonState);
 }
 lastMillis = millis();
}

void setup() {
 Serial.begin(115200);
 pinMode(buttonPin, INPUT_PULLUP);
 pinMode(ledPin,OUTPUT);
 pinMode(ledPin2,OUTPUT);
 attachInterrupt(buttonPin, function_ISR, CHANGE);
 digitalWrite(ledPin, buttonState);
}

void loop() {
 // Code ...

 digitalWrite(ledPin, HIGH);
 delay(1000);
 digitalWrite(ledPin, LOW);
 delay(1000);

  if(buttonState == HIGH)
  {
    Serial.print(buttonState);
    digitalWrite(ledPin2, HIGH);
  }
  else
  {
    Serial.print(buttonState);
    digitalWrite(ledPin2, LOW);
  }

}