mobileapp/screens/test.js

var ShiftStrings = ["Shift 1 (23:00 - 07:00)", "Shift 2 (07:00 - 15:00)", "Shift 3 (15:00 - 23:00)"];
var ShiftTimes;
var CurrentDate;
var SelectedDate;
var CurrentShift;
var SelectedShift;

function formatDate(date) {
  var d = new Date(date),
    month = '' + (d.getMonth() + 1),
    day = '' + d.getDate(),
    year = d.getFullYear();

  if (month.length < 2) month = '0' + month;
  if (day.length < 2) day = '0' + day;

  return [year, month, day].join('-');
}

function SetCurrentDate() {
  var datetime = new Date();
  if (datetime.getHours() == 23) {
    datetime.setDate(datetime.getDate() + 1);
  }

  CurrentDate = formatDate(datetime);
  if ($('#ShiftDate').length) {
    SelectedDate = $('#ShiftDate').val();
  } else {
    SelectedDate = CurrentDate;
  }
}

function SetShiftTimes() {
  var datetime = new Date();
  if (datetime.getHours() == 23 || datetime.getHours() < 7) {
    ShiftTimes = Times[0];
    CurrentShift = 0;
  } else if (datetime.getHours() < 15) {
    CurrentShift = 1;
  } else {
    CurrentShift = 2;
  }

  if ($('#Shift').length) {
    SelectedShift = ShiftStrings.indexOf($('#Shift').val());
  } else {
    SelectedShift = CurrentShift;
  }
}

SetShiftTimes();
SetCurrentDate();

$('#prev, #today, #next').on('click', function() {
console.log("Shift Before:" + SelectedShift);
  if (this.id == "prev") {
    SelectedShift = SelectedShift - 1;
    if (SelectedShift < 0) {
      SelectedShift = 2;
      IncrementDate(-1);
    }
  } else if (this.id == "next") {
    SelectedShift = SelectedShift + 1;
    if (SelectedShift > 2) {
      SelectedShift = 0;
      IncrementDate(1);
    }
  } else {
    SelectedShift = CurrentShift;
    SelectedDate = CurrentDate;
  }

document.getElementById('date').innerHTML = "Date: " + SelectedDate;
document.getElementById('shift').innerHTML = "Shift: " + SelectedShift;

  function IncrementDate(i) {
  	console.log("SelectedDate Before:" + SelectedDate);
    var tmpdate = new Date(SelectedDate);
    console.log("tmpDate Before:" + tmpdate);
    console.log("tmpDate Before:" + formatDate(tmpdate));
    
    tmpdate.setDate(tmpdate.getDate() + i);

    console.log("tmpDate After:" + tmpdate);
    console.log("tmpDate After:" + formatDate(tmpdate));

    SelectedDate = formatDate(tmpdate);
    console.log("SelectedDate After:" + SelectedDate);
  }
});



document.getElementById('date').innerHTML = "Date: " + SelectedDate;
document.getElementById('shift').innerHTML = "Shift: " + SelectedShift;