Calculate the minutes between two datetime in Google Sheets with Google AppScript

getMinutes.gs

var dueBy = "A"; // Provide the appropriate column ID
var todayIs = "B" // Provide the appropriate column ID
var resultField = "C"; // Provide the appropriate column ID
var onTrack = "D" // Provide the appropriate column ID

// first sheet
var sheet = SpreadsheetApp.getActiveSpreadsheet().getSheets()[0];

// row range
var startRow = 2; // Mention the range start only
var endRow = sheet.getLastRow();

function getMinutes() {  
  for (var i=startRow; i<(endRow+1); i++) {
    var today = new Date()
    var date = (today.getMonth()+1)+'/'+today.getDate()+'/'+today.getFullYear();
    var time = today.getHours() + ":" + today.getMinutes() + ":" + today.getSeconds();
    var todayDate = date+' '+time;
    // Writing the DateTime to sheets for script efficiency
    sheet.getRange(todayIs + i).setValue(todayDate);

    var todayDateTime = new Date(sheet.getRange(todayIs + i).getValue());
    var dueDate = new Date(sheet.getRange(dueBy + i).getValue());
    // This calculates the milliseconds
    // We divide it by 1000 and by 60 to get minutes
    var minutesBeforeDue = parseInt((dueDate - todayDateTime) / 1000 / 60);

   // Setting values to the appropriate row
    sheet.getRange(resultField + i).setValue(minutesBeforeDue);
    }
  }
}