CODEWITHSUNDEEP
javascript
sunil_mlec
sunil_mlec

Reputation: 680

day of the year to date in a loop

I am trying to get date from day of the month in a loop. The code works for the first few days, and from then on it is returning random dates.

Any help here?

var now = new Date();
var initDate = new Date(now.getYear() + 1900, 0);

for (var i = 1 ; i <366 ; i++) {
    var day = dateFromDay(i, initDate);
    document.write(" Day " + i + " : " + day);
    document.write("<br>");
}

function dateFromDay(day, initDate) {
    var months = [ "Jan", "Feb", "Mar", "Apr", "May", "Jun", 
                   "Jul", "Aug", "Sep", "Oct", "Nov", "Dec" ];

    var cur = new Date(initDate.setDate(day));
    cur = months[cur.getMonth()] + " " + cur.getDate();
    return cur;
}

Output:

...
...
Day 29 : Jan 29
Day 30 : Jan 30
Day 31 : Jan 31
Day 32 : Feb 1
// From here the output gets messed  up
Day 33 : Mar 4
Day 34 : Apr 3
Day 35 : May 5
Day 36 : Jun 5
Day 37 : Jul 7
Day 38 : Aug 7
Day 39 : Sep 8
Day 40 : Oct 10
Day 41 : Nov 10
Day 42 : Dec 12
Day 43 : Jan 12
Day 44 : Feb 13
...
...

Upvotes: 2

Views: 327

Answers (3)

Pointy
Pointy

Reputation: 413712

Calling setDate() on your "initDate" variable updates that date. Thus, as soon as you overflow January into February, the next call will immediately spill into the next month.

You don't need the "initDate" variable. Start with a freshly-constructed date on each call to the function for the current year, month of January (0), and whatever day number you want. The resulting Date instance will be your date.

Thus:

function dayNumberToDate( dayNumber ) {
  var thisYear = new Date().getFullYear(); // no need to add 1900
  return new Date(thisYear, 0, dayNumber);
}

alert(dayNumberFromDate( 271 )); // alerts Thu Sep 27 2012 00:00:00 GMT-0500 (CDT) (for me)

Upvotes: 1

Abubakkar
Abubakkar

Reputation: 15644

Move the code given below inside your for loop before this line var day = dateFromDay(i, initDate);

 var now = new Date();
 var initDate = new Date(now.getYear() + 1900, 0);

Upvotes: 0

Nelson Ben&#237;tez Le&#243;n
Nelson Ben&#237;tez Le&#243;n

Reputation: 50563

Change your following line:

var cur = new Date(initDate.setDate(day));

for this one:

var cur = new Date();
cur.setDate( initDate.getDate()+day );

Upvotes: 0

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