What If My LED Doesn't Blink? Answered
If you're using an ESP8266 12E with NodeMCU, then 0 corresponds to GPIO0, which is pin D3. You can bridge an LED to ground to verify blinking. The on-board LED's on some versions (I'm using a 12e) are connected to the TX/RX UART pins, so if you program them to drive the LED, you'll not be able to upload your sketches without holding down the flash button, which is slightly inconvenient. If you get advanced and need the pin, it's there for you, though.