Moment.js - How To Detect Daylight Savings Time And Add One Day

Question

I need to create Date Objects from strings of Date data for every hour of every day since the year 2000.

The strings look like this for every hour, in a Month/Day/Year Hour format...

"04/02/2000 01", "04/02/2000 02", "04/02/2000 03" ...all the way to... "04/02/2000 24"

Now, I have the following code, which works fine except for on days with Daylight Savings Time...

  // Split At Space
var splitDate = "04/02/2000 24".split(/[ ]+/);
var hour = splitDate[1];
var day  = splitDate[0];
  // Split At Slashes
var dayArray = day.split("/");
if (hour === "24") {
       // Months are zero-based, so subtract 1 from the month
     date = new Date(Date.UTC( dayArray[2], parseInt(dayArray[0] - 1), dayArray[1], 0, 0, 0 ));
     date.setDate(date.getDate() + 1);
} else {
     // Months and Hours are zero-based, so subtract 1 from each
     date = new Date(Date.UTC( dayArray[2], parseInt(dayArray[0] - 1), dayArray[1], hour, 0, 0 ));
};

On days with daylight savings time, like 04/02/2000 adding a day does not work if the hour is 24. Instead, it just returns Sun, 02 Apr 2000 23:00:00 GMT

With Moment.js, is it possible to detect a DST day and get this code to work correctly?

Answer 1

To detect DST, use the .isDST() method: http://momentjs.com/docs/#/query/is-daylight-saving-time/

moment([2011, 2, 12]).isDST(); // false, March 12 2011 is not DST
moment([2011, 2, 14]).isDST(); // true, March 14 2011 is DST

Using this test, you should be able to determine how to modify your program's behavior accordingly.

Answer 2

Here's how I made a little checker:

var curDst = dtdate.isDST()
var prevDst = moment(dtdate).clone().subtract(1, "day").isDST();
var nextDst = moment(dtdate).clone().add(1, "day").isDST();
var isDstChangeDate = (curDst !== nextDst) === true || (curDst === prevDst) !== true;