esp8266 builtin led

1void setup() {
2  pinMode(LED_BUILTIN, OUTPUT);     // Initialize the BUILTIN_LED pin as an output
3 
4}
5
6// the loop function runs over and over again forever
7void loop() {
8  digitalWrite(LED_BUILTIN, LOW);   // Turn the LED on (Note that LOW is the voltage level
9                                    // but actually the LED is on; this is because 
10                                    // it is acive low on the ESP-01)
11  
12  delay(100);                      // Wait for a second
13  digitalWrite(LED_BUILTIN, HIGH);  // Turn the LED off by making the voltage HIGH
14  
15  delay(100);                      // Wait for two seconds (to demonstrate the active low LED)
16}