Arduino Milis() and Micros() without Delay

https://rudysarduinoprojects.wordpress.com/2019/02/10/fun-with-arduino-13-timer-with-millis-no-delay-multitasking/

#define INTERVAL_1 200  // [ms]
#define INTERVAL_2 1100  // [ms]
byte led_1;
byte led_2;
unsigned long time_for_action_1;
unsigned long time_for_action_2;

void setup() {
  pinMode(8, OUTPUT);
  pinMode(9, OUTPUT);
}

void loop() {
  if (millis() > time_for_action_1) {
    time_for_action_1 = millis() + (unsigned long)INTERVAL_1;
    led_1 = !led_1;
    digitalWrite(8, led_1);
  }
  if (millis() > time_for_action_2) {
    time_for_action_2 = millis() + (unsigned long)INTERVAL_2;
    led_2 = !led_2;
    digitalWrite(9, led_2);
  }
}