how to calculate the difference b/w two dates in js code example

Example 1: javascript difference between two dates

const date1 = new Date('7/13/2010');
const date2 = new Date('12/15/2010');
console.log(getDifferenceInDays(date1, date2));
console.log(getDifferenceInHours(date1, date2));
console.log(getDifferenceInMinutes(date1, date2));
console.log(getDifferenceInSeconds(date1, date2));

function getDifferenceInDays(date1, date2) {
  const diffInMs = Math.abs(date2 - date1);
  return diffInMs / (1000 * 60 * 60 * 24);
}

function getDifferenceInHours(date1, date2) {
  const diffInMs = Math.abs(date2 - date1);
  return diffInMs / (1000 * 60 * 60);
}

function getDifferenceInMinutes(date1, date2) {
  const diffInMs = Math.abs(date2 - date1);
  return diffInMs / (1000 * 60);
}

function getDifferenceInSeconds(date1, date2) {
  const diffInMs = Math.abs(date2 - date1);
  return diffInMs / 1000;
}

Example 2: js calculate date difference

var DateDiff = {

    inDays: function(d1, d2) {
        var t2 = d2.getTime();
        var t1 = d1.getTime();

        return parseInt((t2-t1)/(24*3600*1000));
    },

    inWeeks: function(d1, d2) {
        var t2 = d2.getTime();
        var t1 = d1.getTime();

        return parseInt((t2-t1)/(24*3600*1000*7));
    },

    inMonths: function(d1, d2) {
        var d1Y = d1.getFullYear();
        var d2Y = d2.getFullYear();
        var d1M = d1.getMonth();
        var d2M = d2.getMonth();

        return (d2M+12*d2Y)-(d1M+12*d1Y);
    },

    inYears: function(d1, d2) {
        return d2.getFullYear()-d1.getFullYear();
    }
}

var dString = "May, 20, 1984";

var d1 = new Date(dString);
var d2 = new Date();

document.write("<br />Number of <b>days</b> since "+dString+": "+DateDiff.inDays(d1, d2));
document.write("<br />Number of <b>weeks</b> since "+dString+": "+DateDiff.inWeeks(d1, d2));
document.write("<br />Number of <b>months</b> since "+dString+": "+DateDiff.inMonths(d1, d2));
document.write("<br />Number of <b>years</b> since "+dString+": "+DateDiff.inYears(d1, d2));