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javascriptdatedatepickerdrop-down-menuleap-year

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

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.

Solution

  • 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)