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173

Javascript: calculate number of days in month for a given year

rated 0 times [ 180] [ 7] / answers: 1 / hits: 39735 / 14 Years ago, thu, february 3, 2011, 12:00:00

I have a HTML page with 3 dropdowns for the month, day and year and I was wondering if there was a way to populate the month drop down properly depending on the month and year.

I haven't done this before on the client side, but it looks like a lot of controls like the jQuery DatePicker are doing that behind the scenes.

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kevonmoisesf

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answered 14 Years ago bethv · Accepted Answer

You can play with date objects:

var monthStart = new Date(year, month, 1);

var monthEnd = new Date(year, month + 1, 1);

var monthLength = (monthEnd - monthStart) / (1000 * 60 * 60 * 24)

Arithmetic with Date objects gives a number of milliseconds.

This will even work for December; the Date constructor handles out-of-range arguments by wrapping around.

Note that month is zero-based (it must be between 0 and 11)