function console(msg) {
  var pre = document.createElement('pre')
  pre.innerHTML = msg
  document.body.appendChild(pre)
}

function getFeedbackTime(feedbackTimestamp) {
	/*
  	Note: timestamp structure
     2018 - 03 - 26  T  1 4  :  2 7  :  4 8  .  5 0 8  Z
     01234 567  8910   111213  141516  171819  202122 2324
  */
  
  //compare timestamps only when length equals 24
  if(feedbackTimestamp.length === 24) {
  	//variables
  	let currentTimestamp = new Date().toISOString()
    const feedback_year = feedbackTimestamp.substring(0,4)
  	const current_year = currentTimestamp.substring(0,4)
    const feedback_month = feedbackTimestamp.substring(5,7)
  	const current_month = currentTimestamp.substring(5,7)
    const feedback_day = feedbackTimestamp.substring(8,10)
    const current_day = currentTimestamp.substring(8,10)
    const feedback_hour = feedbackTimestamp.substring(11,13)
    const current_hour = currentTimestamp.substring(11,13)
    const feedback_minute = feedbackTimestamp.substring(14,16)
    const current_minute = currentTimestamp.substring(14,16)
    const feedback_second = feedbackTimestamp.substring(17,19)
    const current_second = currentTimestamp.substring(17,19)
    console(currentTimestamp)
    console(feedbackTimestamp)
    
    //years
    if(current_year !== feedback_year) {
    	const current_year_number = parseInt(current_year)
      const feedback_year_number = parseInt(feedback_year)
      const year_diff = current_year_number-feedback_year_number
      if(year_diff > 1) {
      	console(year_diff+' years ago')
      } else if(year_diff < 0) {
      	console(year_diff+' year(s) ahead : invalid scenario')
      } else {
      	console(year_diff+' year ago')
      }
    } else if(current_month !== feedback_month){
    	//months
      const current_month_number = parseInt(current_month)
      const feedback_month_number = parseInt(feedback_month)
      const month_diff = current_month_number - feedback_month_number
      if(month_diff > 1) {
      	console(month_diff+' months ago')
      } else if(month_diff < 0) {
      	console(month_diff+' month(s) ahead : invalid scenario')
      } else {
      	console(month_diff+' month ago')
      }
    } else if(current_day !== feedback_day) {
    	//days
      const current_day_number = parseInt(current_day)
      const feedback_day_number = parseInt(feedback_day)
      const day_diff = current_day_number - feedback_day_number
      if(day_diff > 1) {
      	console(day_diff+' days ago')
      } else if(day_diff < 0) {
      	console(day_diff+' day(s) ago : invalid scenario')
      } else {
      	console(day_diff+' day ago')
      }
    } else if(current_hour !== feedback_hour) {
    	//hours
      const current_hour_number = parseInt(current_hour)
      const feedback_hour_number = parseInt(feedback_hour)
      const hour_diff = current_hour_number - feedback_hour_number
      if(hour_diff > 1) {
      	console(hour_diff+' hours ago')
      } else if(hour_diff < 0) {
      	console(hour_diff+' hour(s) ahead : invalid scenario')
      } else {
      	console(hour_diff+' hour ago')
      }
    } else if(current_minute !== feedback_minute) {
    	//minutes
      const current_minute_number = parseInt(current_minute)
      const feedback_minute_number = parseInt(feedback_minute)
      const minute_diff = current_minute_number - feedback_minute_number
      if(minute_diff > 1) {
      	console(minute_diff+' minutes ago')
      } else if(minute_diff < 0) {
      	console(minute_diff+' minute(s) ahead : invalid scenario')
      } else {
      	console(minute_diff+' minute ago')
      }
    } else if(current_second !== feedback_second) {
    	//seconds
      const current_second_number = parseInt(current_second)
      const feedback_second_number = parseInt(feedback_second)
      const second_diff = current_second_number - feedback_second_number
      if(second_diff > 1) {
      	console(second_diff+' seconds ago')
      } else if(second_diff < 0) {
      	console(second_diff+' second(s) ahead : invalid scenario')
      } else {
      	console(second_diff+' second ago')
      }
    } else if(current_year === feedback_year) {
        console('just now')
    }
    
  }
  else {
  	console('timestamps can\'t be compared')
  }
}

getFeedbackTime('2018-03-26T16:09:45.291Z')