const byte ledPin=6;
const byte interruptPin=2;
volatile bool buttonFlag=false;
volatile bool buttonStable=false;
const long debounceTime=100; //debouncing time, ms
volatile unsigned long prevMillis;

void setup() {
  Serial.begin(9600);

  pinMode(ledPin,OUTPUT);
  pinMode(interruptPin,INPUT_PULLUP);
  digitalWrite(ledPin,LOW);
  
  attachInterrupt(digitalPinToInterrupt(interruptPin),buttonISR,CHANGE);
}

void loop() {
  delay(500);
  if (buttonFlag) {
    digitalWrite(ledPin,HIGH);
    delay(10);
    digitalWrite(ledPin,LOW);
    buttonFlag=false;
  }
}

void buttonISR() {
    if((long)(millis()-prevMillis)>=debounceTime) {
    prevMillis=millis(); //same value; millis does not advance during interrupts
    buttonFlag=true;
  }
}