test.js

let delay = (ms) => {
  return new Promise( (resolve, reject) => {
    setTimeout(() => { resolve(); }, ms);
  });
};

let digitalRead = (thePin) => {
  return new Promise((resolve, reject) => {
    gBoard.digitalRead(thePin, function(value){
      resolve(value);
    });
  });
};

let  digitalReadPromise = (pin) => {
  return delay(10).then(digitalRead.bind(null, pin));
};

setInterval(() => {
  digitalReadPromise(START_BUTTON).then((start_button_value) => {
    if(start_button_value == 0){
      return digitalReadPromise(CALIBRATE_FANS_BUTTON_PIN);
    }
    else{
      return -1;
    }
  }).then((calibrate_button_value) => {
    if(calibrate_button_value == 0){
      // do the calibrate function
    }
    else if(calibrate_button_value == 1){
      // do the normal functino
    }
  });
}, 100);