mbta.js

const mbtapi = require('mbtapi').create({
  apiKey: process.env.MBTA_API_KEY,
});

function arrivalTimes(stopId) {
  return mbtapi.predictionsByStop(stopId).then(function (predictions) {
    const trips = predictions.mode[0].route[0].direction[0].trip;
    return trips.map(trip => {
      var predictionDate = new Date();
      predictionDate.setSeconds(predictionDate.getSeconds() + Number(trip.pre_away));
      return predictionDate;
    });
  });
}

export const massAveEta = { forestHills: [], oakGrove: [] };

function updateMassAveEta() {
  arrivalTimes('70013').then(times => {
    massAveEta.oakGrove = times;
  }).catch(() => {
    massAveEta.oakGrove = null;
  });

  arrivalTimes('70012').then(times => {
    massAveEta.forestHills = times;
  }).catch(() => {
    massAveEta.forestHills = null;
  });
}

// Update the eta on an interval
updateMassAveEta();

const interval = Number(20000);
setInterval(updateMassAveEta, interval);