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How to get the exact quantity of months between two dates?

I'm trying to get the quantity of months between two dates
but for some reason, the moment diff method some times returns the correct number and some times is wrong (by one month), (depending on the dates I guess)
var estDate = "some date"; //2022-06-02
estDate = estDate.toString();
var estDateYear = estDate.substring(0,4);
var estDateMonth = estDate.substring(4, 6);
var estDateDay = estDate.substring(6, 8);
estDate = estDateYear + '-' + estDateMonth + '-' + estDateDay;
//first date
estDate = moment(estDate);
//actual date
var date = moment();
//DIFF
var diff= date.diff(estDate, 'month');
diff= diff.toString();
Any Idea why this happens?

You should set the third argument in the diff method to true. This will return fractions of a month instead of a whole number. Then, you can round as needed to return the number you would like.
var diff = Math.floor(date.diff(estDate, 'month', true));
Documentation
https://momentjs.com/docs/#/displaying/difference/
By default, moment#diff will truncate the result to zero decimal places, returning an integer. If you want a floating point number, pass true as the third argument.

Why not just parse the estDate string using moment to begin with?
var estDate = "2022-06-02"; //2022-06-02
estDate = moment(estDate, "YYYY-MM-DD");
//actual date
var date = moment();
//DIFF
var diff= date.diff(estDate, 'month');
diff= diff.toString();

// Simply use Momentjs Formation library
//let estDate = "2022-06-02";
let estDate = moment("2022-06-02", "YYYY-MM-DD");
let actualdate = moment();
let diff= actualdate.diff(estDate, 'M');
diff= diff.toString();
console.log(diff);
<div>
<script src="//cdnjs.cloudflare.com/ajax/libs/moment.js/2.10.3/moment.min.js"></script>
</div>

Set last day of month on YYYYMM date format - Javascript

I've a variable that has value of date in YYYYMM format. For example:
var givenDate = "201704"
How can I find out the last day of the given month and append to it. For example,
//last day of 2017 04 (April) is 30th so append value to givenDate + lastDate;
//that will be 20170430
var newFullGivenDate = "20170430";

const date = "201704";
const year = parseInt(date.substring(0, 4));
const month= parseInt(date.substring(4, 6));
const lastDay = (new Date(year, month, 0)).getUTCDate();
const newFullGivenDate = date + lastDay;
console.log(newFullGivenDate);

var givenDate = "201704";
var month = givenDate.substring(4, givenDate.length); // retrieves 04
var year = givenDate.substring(0, 4); // retrieves 2017
var d = new Date(year, month, 0);
alert(d.getDate());
Reference: MDN

To achieve expected result, use below option
last day of month - new Date(year,month ,0)
var givenDate = "201704";
var currDate = new Date(givenDate.substr(0,3),givenDate.substr(4) ,0)
var newFullGivenDate = givenDate + currDate.getDate();
console.log(newFullGivenDate)
Codepen URL for reference - https://codepen.io/nagasai/pen/OmgZMW

I would break it down into two functions:
// Get last day from year and month
let lastDayOf = (year, month) => (new Date(year, month, 0)).getDate();
// Add last day to string only if input is correct
let addLastDay = (input) => {
// In case you pass number (201705) instead of string ("201705")
if (Number.isInteger(input)) input = input.toString();
// Check if input is in correct format - 6 digit string
if (typeof input !== "string" || !input.match(/^\d{6}$/)) {
return input; // You can implement desired behavour here. I just return what came
}
const year = input.substr(0, 4);
const month = input.substr(4, 2);
return input + lastDayOf(year, month);
}
// Tests
console.assert(addLastDay("201704"), "20170430");
console.assert(addLastDay("201702"), "20170228");
console.assert(addLastDay("201202"), "20120229");
console.assert(addLastDay(201705), "20170531");
console.assert(addLastDay(20170), 20170); // Wrong input
// Interactive example
document.getElementsByTagName('button')[0].addEventListener('click', () => {
let input = document.getElementsByTagName('input')[0];
input.value = addLastDay(input.value);
});
<input type="text" value="201704"><button>Calculate</button>

If you are using moment js you can yry this:
var date = moment(newFullGivenDate ).format('YYYYMMDD');
date = date.add(-1 * parseInt(date.format('DD')), 'days').add(1, 'months');

angularjs - calculate a date plus one day

I need to get the date one day after another date.
I do :
$scope.date2.setDate($scope.date1.getDate()+1);
if
$scope.date1 = 2015-11-27
then
$scope.date2 = 2015-11-28
It s ok,
but when
$scope.date1 = 2015-12-02
then
$scope.date2 = 2015-11-28 (ie tomorrow)
I don't understand why...
If anyone knows..

try this instead efficient simple pure JS
var todayDate = new Date();
console.log(new Date().setDate(todayDate.getDate()+1));
so you will have that same Date type object and hence you don't need to go with moment.js

Use moment.js for this momentjs
var startdate = "2015-12-02";
var new_date = moment(startdate, "YYYY-MM-DD").add('days', 1);
var day = new_date.format('DD');
var month = new_date.format('MM');
var year = new_date.format('YYYY');
alert(new_date);
alert(day + '.' + month + '.' + year);

How to convert javascript string format to date

In my ajax success I am getting result.Date as "/Date(-2208967200000)/". I need to check with the following date and proceed..
How to convert the "/Date(-2208967200000)/" to "01-01-1900" for below if condition?
if (result.Date != "01-01-1900") {
....
}

You can convert result.Date into you comparison date format, same as below example
var dateString = "\/Date(-2208967200000)\/".substr(6);
var currentTime = new Date(parseInt(dateString ));
var month = currentTime.getMonth() + 1;
var day = currentTime.getDate();
var year = currentTime.getFullYear();
var date = day + "/" + month + "/" + year;
After doing this.. you can compare it with other date..

Reference
var jsonDate = "/Date(-2208967200000)/";
var date = new Date(parseInt(jsonDate.substr(6)));
alert(date);
The substr function takes out the "/Date(" part, and the parseInt function gets the integer and ignores the ")/" at the end. The resulting number is passed into the Date constructor.
jQuery dateFormat is a separate plugin. You need to load that explicitly using a tag.

You could use a regex to get the value between the brackets and then pass that to the Date():
var input = "/Date(-2208967200000)/";
var matches = /\(([^)]+)\)/.exec(input);
var date = new Date(parseInt(matches[1], 10));
Example fiddle

calculate difference between two timestamp and get difference in unix timestamp

I want to calculate the difference between two dateTime, one date is submitted by user and other is current time:
user submitted time - now = difference in unix
user submitted time format is:
2014-03-26 10:52:00
Thanks for your help.

You can simply do this with getTime() which returns the number of milliseconds.
var ds = "2014-03-26 10:52:00";
var newDate = new Date(ds).getTime(); //convert string date to Date object
var currentDate = new Date().getTime();
var diff = currentDate-newDate;
console.log(diff);
Sometimes there are chance for cross browser compatibility in parsing the date string so it is better to parse it like
var ds = "2014-03-26 10:52:00";
var dateArray = ds.split(" "); // split the date and time
var ds1 = dateArray[0].split("-"); // split each parts in date
var ds2 = dateArray[1].split(":"); // split each parts in time
var newDate = new Date(ds1[0], (+ds1[1] - 1), ds1[2], ds2[0], ds2[1], ds2[2]).getTime(); //parse it
var currentDate = new Date().getTime();
var diff = currentDate - newDate;
console.log(diff); //timestamp difference

You can use MomentJS library
var user_submited_time = moment('2014-03-26 10:52:00');
var now = moment();
var value = user_submited_time - now;