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Editorial Team
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Asked: 2026-05-22T22:54:03+00:00

I’m working with javascript Date objects and seeing very odd behavior. If I keep

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I’m working with javascript Date objects and seeing very odd behavior. If I keep setting a date object to another date object + an offset, it starts adding 30 days or so. If I reset the date object in between attempts or if I do the date math on the same object it works as expected.

Probably easier to see the test bed I’m running in the latest chrome/ff:

var date = new Date();
console.log("start:", date);

var test = new Date();
test.setDate( date.getDate() + 1 );
console.log("test1:", date, test);
test.setDate( date.getDate() + 1 );
console.log("test2:", date, test);
test.setDate( date.getDate() + 1 );
console.log("test3:", date, test);

test = new Date();
test.setDate( date.getDate() + 1 );
console.log("test reset 1:", date, test);
test = new Date();
test.setDate( date.getDate() + 1 );
console.log("test reset 2:", date, test);
test = new Date();
test.setDate( date.getDate() + 2 );
console.log("test reset 3:", date, test);

test = new Date();
test.setDate( test.getDate() + 1 );
console.log("test selfref 1:", test);
test.setDate( test.getDate() + 1 );
console.log("test selfref 2:", test);

And the output I get:

"start:" Tue May 31 2011 13:09:13 GMT-0400 (EDT)
"test1:" Tue May 31 2011 13:09:13 GMT-0400 (EDT) Wed Jun 01 2011 13:09:13 GMT-0400 (EDT)
"test2:" Tue May 31 2011 13:09:13 GMT-0400 (EDT) Sat Jul 02 2011 13:09:13 GMT-0400 (EDT)
"test3:" Tue May 31 2011 13:09:13 GMT-0400 (EDT) Mon Aug 01 2011 13:09:13 GMT-0400 (EDT)
"test reset 1:" Tue May 31 2011 13:09:13 GMT-0400 (EDT) Wed Jun 01 2011 13:09:13 GMT-0400 (EDT)
"test reset 2:" Tue May 31 2011 13:09:13 GMT-0400 (EDT) Wed Jun 01 2011 13:09:13 GMT-0400 (EDT)
"test reset 3:" Tue May 31 2011 13:09:13 GMT-0400 (EDT) Thu Jun 02 2011 13:09:13 GMT-0400 (EDT)
"test selfref 1:" Wed Jun 01 2011 13:09:13 GMT-0400 (EDT)
"test selfref 2:" Thu Jun 02 2011 13:09:13 GMT-0400 (EDT)

So you can see that test1-3 the original date object remains the same, but the test object which should always be the original date + 1 day – goes all over the place.

Subsequently the reset tests and the selfref tests seem to work as expected.

Is this a bug or am I misunderstanding something?

felix

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1 Answer

  1. Editorial Team

    You keep adding 32 days from the date.getDate()+1

    If you change to

    var test = new Date();
test.setDate( test.getDate() + 1 );
console.log("test1:", date, test);
test.setDate( test.getDate() + 1 );
console.log("test2:", date, test);
test.setDate( test.getDate() + 1 );
console.log("test3:", date, test);

    You get

    start: Date {Tue May 31 2011 19:21:34 GMT+0200 (CEST)}
test1: Date {Tue May 31 2011 19:21:34 GMT+0200 (CEST)} Date {Wed Jun 01 2011 19:21:34 GMT+0200 (CEST)}
test2: Date {Tue May 31 2011 19:21:34 GMT+0200 (CEST)} Date {Thu Jun 02 2011 19:21:34 GMT+0200 (CEST)}
test3: Date {Tue May 31 2011 19:21:34 GMT+0200 (CEST)} Date {Fri Jun 03 2011 19:21:34 GMT+0200 (CEST)}
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