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Question

Find first day of previous month in javascript

Answer 1

+4 A:

function firstDayInPreviousMonth(yourDate) {
    var d = new Date(yourDate);
    d.setDate(1);
    d.setMonth(d.getMonth() - 1);
    return d;
}

EDIT: Alright... I've definitely learned something here. I think that this is the simplest solution that covers all cases (and yes, it does work for January):

function firstDayInPreviousMonth(yourDate) {
    return new Date(yourDate.getYear(), yourDate.getMonth() - 1, 1);
}

Prestaul 2009-03-03 04:31:55

Note that this will FAIL for something like: firstDayInPreviousMonth(new Date("Mar 31 2009")). See the comments on: http://stackoverflow.com/questions/499838/javascript-date-next-month

Shog9 2009-03-03 04:40:20

It wouldn't fail if he setDate(1) before doing the setMonth()

Paolo Bergantino 2009-03-03 04:46:08

Yes, that works nicely.

Shog9 2009-03-03 04:49:57

Answer 2

+3 A:

The following should work:

now = new Date();
if (now.getMonth() == 0) {
    current = new Date(now.getYear() - 1, 11, 1);
} else {
    current = new Date(now.getYear(), now.getMonth() - 1, 1);
}

keeping in mind that months are zero-based so December is 11 rather than 12.

But, as others have pointed out, the month wraps, even as part of the atomic constructor, so the following is also possible:

now = new Date();
firstDayPrevMonth = new Date(now.getYear(), now.getMonth() - 1, 1);

paxdiablo 2009-03-03 04:34:30

I like this approach, but your solution actually isn't correct. When getMonth() == 1, the month is February. You want to check for getMonth() == 0, and even that isn't required because the Date constructor will accept negative values and work correctly.

Prestaul 2009-03-03 04:39:37

You're neglecting the fact that setMonth will wrap values. Prestaul's answer works fine for January.

overslacked 2009-03-03 04:39:53

Yes, but not for moving back to a month where the number of days is less, unfortunately. It's better to construct the new date atomically rather than piecemeal.

paxdiablo 2009-03-03 04:44:31

Considering the Mar 31 example, you are correct about the anatomical date construction - if you change your answer (I do find the "blindly subtracting a month" line to be misleading given javascript's setXXX wrapping) I'll be happy to adjust my vote on this answer.

overslacked 2009-03-03 04:50:02

Done, overslacked.

paxdiablo 2009-03-03 04:53:07

I agree. You'll get my vote as well if you remove the test for January.

Prestaul 2009-03-03 04:54:57

As you wish ... I had to check it was okay in the constructor as well, rather than just for setMonth().

paxdiablo 2009-03-03 05:00:23

+1... I love StackOverflow because the best answer usually does find its way to the top!

Prestaul 2009-03-03 05:02:39

Answer 3

A:

JavaScript Get Month

http://java.pakcarid.com/Cpp.aspx?sub=373&ff=2976&topid=39&sls=25

lois 2010-10-23 07:43:47

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Find first day of previous month in javascript

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