MOD-WIFI-ESP8266(REV.B) and the button

[Chis]

I am using a MOD-WIFI-ESP8266(REV.B) board with the button. Can I use that button when the program is running to perform some action after the button is pressed?

[LubOlimex]

Yes.

The button is connected to GPIO0 which is also used for initial boot configuration. When GPIO0 is in low/GND position then the serial bootloader mode would trigger (for serial upload); when GPIO0 is high/VCC then normal execution mode would start. Once the board boots in the desired mode, the button can be used as general-purpose button.