int ledPin1 = D2;
int ledPin2 = D4;
int currLit, currOff, temp;

void setup() {
    // We want to tell the Argon that we'll use
    // D2 and D4 as output pins.
    pinMode(ledPin1, OUTPUT);
    pinMode(ledPin2, OUTPUT);
    currLit = ledPin1;
    currOff = ledPin2;
}

void loop() {
    // First... On
    digitalWrite(currLit, HIGH);   // Turn ON the LED pins

    // Now... Off
    digitalWrite(currOff, LOW);   // Turn OFF the LED pins
    delay(1000);               // Wait for 1000mS = 1 second
    // rinse + repeat
    
    temp = currLit;
    currLit = currOff;
    currOff = temp;

}