Calculate difference between two dynamic dates in Javascript

Question

I'm trying to calculate the number of days between two dynamic dates.

I have a product where credits are renewed the day 19th, and I want to show the user how many days remain to renew them.

I have tried this code with no success: if today it's November 22nd, the result that this code returns is a negative number, when it should return "27" as there are 27 days between today and December 19th.

var today = new Date();
var todayMonth = today.getMonth()+1;
if(todayMonth<10) todayMonth = 0+todayMonth;
var datetwo = new Date(today.getFullYear()+"-"+todayMonth+"-19T00:00:00.000Z");
var dayDif = (datetwo - today)  / 1000 / 60 / 60 / 24;
dayDif = Math.ceil(dayDif);

var daysLeftRenew = dayDif;

I also tried with Moment.js, but I cannot find how to work with dynamic dates like this.

Answer 1

if today it's November 22nd, the result that this code returns is a negative number, when it should return "27" as there are 27 days between today and December 19th.

You need to change this line

var todayMonth = today.getMonth()+1;

to

var todayMonth = today.getMonth()+2;//2 instead of 1 as getMonth will give value starting from 0 to 11.

since you are setting the month parameter within the string format and it will take the month parameter as is.

Demo

 var today = new Date(); var todayMonth = today.getMonth() + 2; if (todayMonth < 10) todayMonth = 0 + todayMonth; var datetwo = new Date(today.getFullYear() + "-" + todayMonth + "-19T00:00:00.000Z"); var dayDif = (datetwo - today) / 1000 / 60 / 60 / 24; dayDif = Math.ceil(dayDif); var daysLeftRenew = dayDif; console.log(daysLeftRenew); 

Answer 2

Dates manipulation may be tricky, you can consider using dedicated library for such computations like moment.js . It will also make code code much more clean:

 var targetDate = moment().date(19); if (targetDate.isBefore(moment())) { targetDate.add(1, 'month'); } console.log(targetDate.endOf('day').fromNow()); 

 <script src="https://cdnjs.cloudflare.com/ajax/libs/moment.js/2.19.2/moment.min.js"></script>