I'm refering to the page here
The example code is incorrect. The example shows led state change in pin 13 when interrupt occurs, but the interrupt is attached to pin 13 instead of external interrupt pin 2 or3
Here is the corrected code.
const int pin = 13;
const int interruptPin = 2;
volatile int state = LOW;
void setup() {
pinMode(pin, OUTPUT);
attachInterrupt(digitalPinToInterrupt(interruptPin), blink, CHANGE);
}
void loop() {
digitalWrite(pin, state);
}
void blink() {
state = !state;
}