NodeMCU: Blink

#define LED D0             // Led in NodeMCU at pin GPIO16 (D0).
void setup() {
   pinMode(LED, OUTPUT);   // LED pin as output.
}
void loop() {
   digitalWrite(LED, HIGH);// turn the LED off.(Note that LOW is the voltage level but actually 
                           //the LED is on; this is because it is acive low on the ESP8266.
   delay(1000);            // wait for 1 second.
   digitalWrite(LED, LOW); // turn the LED on.
   delay(1000);            // wait for 1 second.
}