const int LED_PIN = LED_BUILTIN;
const int BUTTON_PIN = D2;

void setup() {
  pinMode(LED_PIN, OUTPUT);
  pinMode(BUTTON_PIN, INPUT_PULLUP);
}

void loop() {
  int buttonState = digitalRead(BUTTON_PIN);

  if (buttonState == LOW) {
    digitalWrite(LED_PIN, HIGH);
  } else {
    digitalWrite(LED_PIN, LOW);
  }
}