How to check the difference between dates

Question

I created a function to check the difference between a particular date and the current date, everything is working perfectly for past dates. But, when it comes to future dates, it gives the correct difference eg. the 18th of May is two days after the 16th of May, so the difference is 2, but I don't know if it's two days before or two days after. I cannot differentiate between future dates and past dates, whether the date is in the past or in the future. here is my code:

function GetDateDiff(previousDate, previousTime) {
  let today = new Date();
  let dd = String(today.getDate()).padStart(2, "0");
  let mm = String(today.getMonth() + 1).padStart(2, "0"); //January is 0!
  let yyyy = today.getFullYear();

  let currentDate = mm + "/" + dd + "/" + yyyy; // this will give you the current date
  let previousMinutes = previousTime.split(":")[1];
  let previousSeconds = previousTime.split(":")[2];
  let previousHours = previousTime.split(":")[0];

  let timePeriod = "seconds"; // timePeriod is the current unit of mesearement whether in seconds hours or days
  let timeInNumber = "0"; //timeInNumber is the number infront of the timeperiod eg the 40 in 40 minites is the timeInNumber

  let dateObj = new Date();

  // this is to set the appropriate seconds, minutes and hours
  if (currentDate == previousDate) {
    if (dateObj.getHours() == previousHours) {
      if (dateObj.getMinutes() == previousMinutes) {
        timeInNumber = dateObj.getSeconds() - previousSeconds;
        timePeriod = "Second";
      } else {
        timeInNumber = dateObj.getMinutes() - previousMinutes;
        timePeriod = "Minute";
      }
    } else {
      timeInNumber = dateObj.getHours() - previousHours;
      timePeriod = "Hour";
      // timePeriod =dateObj.getHours();
    }
  } else {
    const previousDateDifferential = new Date(previousDate);
    const currentDateDifferential = new Date(currentDate);
    const differenceInDate = Math.abs(
      currentDateDifferential - previousDateDifferential
    );

    // this is to calculate the difference in days, weeks, months and years
    const diffDays = Math.ceil(differenceInDate / (1000 * 60 * 60 * 24));
    const diffWeeks = Math.ceil(differenceInDate / (1000 * 60 * 60 * 24 * 7));
    const diffMonths = Math.ceil(differenceInDate / (1000 * 60 * 60 * 24 * 7 * 4));
    const diffyears = Math.ceil(differenceInDate / (1000 * 60 * 60 * 24 * 7 * 4 * 12));

    // this is to set the appropriate days, weeks, months and years
    if (diffDays <= 30) {
      timeInNumber = diffDays;
      timePeriod = "Day";
    } else if (diffDays > 30 && diffWeeks <= 4) {
      timeInNumber = diffWeeks;
      timePeriod = "Week";
    } else if (diffWeeks > 4 && diffMonths <= 12) {
      timeInNumber = diffMonths - 2;
      timePeriod = "Month";
    } else if (diffMonths > 12) {
      timeInNumber = diffyears - 1;
      timePeriod = "Year";
    }
  }

  if (timeInNumber > 1) {
    timePeriod += "s"// this is to ad 's' at the end of the time period if the time period is more than 1
  }
  return `${timeInNumber} ${timePeriod} Ago`;
}

if I write GetDateDiff("05/14/2022", "00:00:00") // result will be 2 days ago

if I write GetDateDiff("05/18/2022", "00:00:00") // result will still be 2 days ago, how can i make it 2 days later or check that the date is in the future

Answer 1

The best tip was given already: use > and < to compare dates. Here is an example to get you started:

// function GetDateDiff to get the difference to the current date including negative values
function GetDateDiff(date) {
  // get current date
  var currentDate = new Date();
  // get the difference between the current date and the date passed in
  var diff = date.getTime() - currentDate.getTime();
  // Build string prefix for negative and positive dates
  var diffString = diff < 0 ? "In the Past: " : "In the Future: ";
  // get the absolute value of the difference
  diff = Math.abs(diff);
  // get the days, hours, minutes, and seconds from the difference
  var days = Math.floor(diff / (1000 * 60 * 60 * 24));
  var hours = Math.floor((diff % (1000 * 60 * 60 * 24)) / (1000 * 60 * 60));
  var minutes = Math.floor((diff % (1000 * 60 * 60)) / (1000 * 60));
  var seconds = Math.floor((diff % (1000 * 60)) / 1000);
  // return the difference in days, hours, minutes, and seconds
  return diffString + days + " days, " + hours + " hours, " + minutes + " minutes, " + seconds + " seconds";
}

// example usage
var date = new Date(2020, 0, 1, 0, 0, 0, 0);
var diff = GetDateDiff(date);
alert(diff);

var date = new Date(2024, 0, 1, 0, 0, 0, 0);
var diff = GetDateDiff(date);
alert(diff);