How do I find the number of given days between two dates in Javascript?

Question

I have two arbitrary dates, lets say April 1st 2012 and January 15th 2013. I want to calculate the number of Sundays, Mondays, Tuesdays, Wednesdays, Thursdays, Fridays, and Saturdays between those two dates.

Is there a surefire-quick way to do this without crippling the users CPU/browser?

Thanks

Update

The premise of this is, we have a defined average number of events for any given day of the week. We need to calculate the number of events to happen in a time period, even for partials (like 1/2 day of Sunday would be half the number of events added to total)

Why did you explicitly list all weekdays? There are no days you do not want to count, do you? — Bergi, May 14 '13 at 17:53
No I would like to count all days in the week :) I have found that on here, its best to be explicit in your needs. — Barry Chapman, May 14 '13 at 17:54
looping over the number of days between then and now and incrementing a json object that contains an assortment of the days. — Barry Chapman, May 14 '13 at 17:55
No, the date does not have to be in milliseconds, the nearest second is fine — Barry Chapman, May 14 '13 at 17:56
Find how many full weeks are between your dates and then figure out the remaining days. That would be my approach — Shaded, May 14 '13 at 17:57
Aren't there 86400 seconds in a day? And aren't a lot of Unix timestamps in seconds since epoch? This suggests..... subtraction and division. — Paul, May 14 '13 at 17:59
@Bergi, If I have the seconds between the timestamps I could divide by 607800 to figure out the full weeks, each one of those will increment each day by 1. Then I'm just left to figure out which days I have extras of. Which I haven't thought all the way through. — Shaded, May 14 '13 at 18:01
Added an update. There are no other SO questions that relate to my question — Barry Chapman, May 14 '13 at 18:04
@BarryChapman You may need to go read about the Poisson distribution. This is the usual way one formalizes constant probability of an event per unit time. http://en.wikipedia.org/wiki/Poisson_distribution — Paul, May 14 '13 at 18:05
Also, I would note that some things, like web visits, are not uniform for all days of the week. — Paul, May 14 '13 at 18:06

Chango · Accepted Answer · 2013-05-14T19:10:09.130

2

Ok, here is a possible untested solution

date1 = new Date("2012-02-10");
date2 = new Date("2012-03-10");

daysInBetween = (date2.getTime() - date1.getTime())/1000/3600/24;

dayOfTheWeek1 = date1.getDay();

weeks = parseInt(daysInBetween/7, 10);
extraDays = daysInBetween%7;

You have weeks + 1 days of dayOfWeek1 ... dayOfWeek1 + (6 - extraDays)

You have weeks + 1 + extraDays days of dayOfWeek1 + (6 - extraDays) ... dayOfWeek1 + 6

Please take into acount that if dayOfWeek1 === 6 then I am assuming that dayOfWeek1 + 1 === 0.

EDIT:

A little bit more of code:

var days = {};
var dayOfTheWeekEnd = dayOfTheWeek1 + 6 - extraDays; // no imagination for names...
if (dayOfTheWeekEnd < 6) {
  if (0 >= dayOfTheWeek1 && 0 <= dayOfTheWeekEnd) {
    days.sunday = weeks + 1;
  } else {
    days.sunday = weeks + 1 + extraDays;
  }
  // etc for the other days, a for loog with an i instead of the 0 would be better.
} else {
  // I have to go the school! I'll edit it later.
  // The idea is that you have to take dayOfTheWeekEnd back to the 0-6 range
  // and check if its after dayOfWeek1 or before dayOfTheWeekEnd, then days.sunday=weeks+1.
}

edited May 14 '13 at 19:10

answered May 14 '13 at 18:12

Chango

6,754
1
28
37

Thanks @Scott! The answer has been changed. – Chango May 14 '13 at 18:20
1

[This answer](http://stackoverflow.com/a/544429/260389) has a great solution to OP's problem. – Chango May 14 '13 at 18:25
this is getting me very close - do i need to add a separate line item for each dayOfWeek2,3,4,5,6 etc? – Barry Chapman May 14 '13 at 18:38
I would recomend you use the answer I marked in the comment above, but yes, you could make a method that returns an object with the days for `0` (Sunday I think...), `1`, etc. – Chango May 14 '13 at 18:59

Shaded · Answer 2 · 2013-05-14T18:43:26.730

Thought it through... haven't tested it but I hope it helps.

function(date1, date2) {
   // date1 is assumed to be 12:00:00 am and date2 is actually the date after target at 
   // 12:00:00 am to make the dates inclusive so from the example date1 = 2012/4/1 and
   // date2 = 2013/1/16
   var timeBetween = date2.getTime() - date1.getTime(); //milliseconds between
   var weeks = timeBetween/1000/60/60/24/7;
   var sun = weeks;
   var mon = weeks;
   var tue = weeks;
   var wed = weeks;
   var thu = weeks;
   var fri = weeks;
   var sat = weeks;

   date1.setTime(date1.getTime() + weeks*7*24*60*60*1000); //set the first date to x weeks later
   //if this iterates more than 7 times then something is wrong.
   while(date1.getTime() < date2.getTime()){
       switch(date1.getDay()){
           case 0:
                sun++;
                break;
           case 1:
                mon++;
                break;
           ...
        }
        date1.setTime(date1.getTime() + 1000 * 60 * 60 * 24); //Move date 1 to the next date.
    }
}

How do I find the number of given days between two dates in Javascript?

2 Answers2