javascript date plus some days issue

Question

I am developing a report system. In my report system I am going to automatically plus days to date that picked date. I used following Javascript code snippet.

function add_date(curdate, days) {
  
  //curdate format : "yyyy-mm-dd"
  var newdate = new Date(curdate);

  newdate.setDate(newdate.getDate() + days);

  var dd = newdate.getDate();
  var mm = newdate.getMonth() + 1;
  var y = newdate.getFullYear();

  if(dd < 10)
    dd = '0' + dd;
  if(mm < 10)
    mm = '0' + mm;

  var someFormattedDate = y + '-' + mm + '-' + dd;
  return someFormattedDate;
  
}

This function is working as well on almost platforms and browsers. But on the particular platform or browser like iPhone Safari and Windows 8.1, I got different result. If I plus 3 days, I can get the result that plus 2 days. I tested on my computer, iPhone and browserstack.com. I want kindly your assistance. Thanks.

Your starting Date format, "yyyy-mm-dd", will be interpreted as a UTC time by most modern browsers, but not on *all* browsers. That can make a difference because midnight on that date may be the day before in your time zone. — Pointy, Feb 18 '16 at 20:46
Possible duplicate of [Add days to DateTime](http://stackoverflow.com/questions/563406/add-days-to-datetime) — WhiteHat, Feb 18 '16 at 21:00

score 1 · Answer 1 · answered Feb 18 '16 at 20:56

1

I'd say your best bet would be to look into Moment.js

But you might try something like this...

// add 5 days
console.log(add_date('2016-02-18T15:53:02Z', 5));

function add_date(curdate, days) {
    var newdate = new Date(curdate);

    // add number of days
    return new Date(newdate.getTime() + ((24 * 60 * 60 * 1000) * days));
}

answered Feb 18 '16 at 20:56

WhiteHat

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lots of things to consider, UTC, daylight savings time, etc. -- Moment.js could handle... – WhiteHat Feb 18 '16 at 20:56
Thanks for you post. Then I want to return date format as "yyyy-mm-dd". – ZhangyuWang Feb 18 '16 at 22:05

score 0 · Answer 2 · answered Feb 18 '16 at 22:55

The date problem is probably because of time zone interpretations.

The date string 'yyyy-mm-dd' is supposed to mean midnight UTC, but some browsers may not respect this convention.

To work around this issue, you can do a quick fix by appending a fixed time to your date string.

Adding this:

  curdate += 'T12:00:00Z';

will definitely set the time to noon UTC.

jsfiddle here

score 0 · Answer 3 · answered Feb 19 '16 at 00:14

As pointed out in other answers, ECMAScript 2015 requires y-m-d format to be parsed as UTC, however there was a time when ECMCAScript 2015 was interpreted as treating it as local (per ISO 8601 and long format date and time strings without a timezone), however that interpretation was reversed (note that ISO 8601 format date and time without a timezone is treated as local).

Also, not all browsers in use correctly parse ISO formats, and some don't parse them at all.

If you are west of Greenwich, then new Date('2016-02-20') will create a date for local 19 February, not 20, which might be confusing.

You don't say whether you want it to be local or not, but since this is for reporting perhaps it should be. You can use a library to do the parsing, but it only takes a couple of lines of code:

/*  Parse and validate a date in format yyyy-mm-dd
**  Note that a date without a timezone is treated as LOCAL, per ISO 8601
**  @param {string} s - date in format y-m-d
**  @returns {Date} time vlaue is NaN if date is invalid
*/
function parseISODateLocal(s){
  var b = s.split(/\D/);
  var d = new Date(b[0], --b[1], b[2]);
  return d && d.getMonth() == b[1]? d : new Date(NaN);
}

To format a date as y-mm-dd, you can use:

/* Return an ISO 8601 string without timezone
** @param {Date} d - date to create string for
** @returns {string} string formatted as ISO 8601 without timezone
*/
function toISODateLocal(d) {
  function z(n){return (n<10?'0':'') + n}
  return d.getFullYear() + '-' + z(d.getMonth()+1) + '-' + z(d.getDate());
}

javascript date plus some days issue

3 Answers3