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Asked: 2026-05-24T18:37:38+00:00

Why is this returning the 31st instead of the 1st ? As I understand

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Why is this returning the 31st instead of the 1st? As I understand it, the UTC method requires 3 parameters ( full year, month, day ), and the day parameter must be an integer between 1 – 31. Because getDate() returns with an integer between 0 and 31, I also suspected 0 would be a possibility.

firstDay = new Date(Date.UTC( 2011 , 7 , 1 )).getDate(); 
// returns 31 (last day of this month)

Let me clarify and say, this is not a special case. With the day parameter as 2, 3, or 4, this will return 1, 2, 3, and so on.

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1 Answer

  1. Editorial Team

    Your timezone offset is negative so like -4. So 7/1/2011 at 12:00AM minus 4 hours is 6/31/2011 8:00PM. Date.UTC takes additional parameters that you can use to pass hours, minutes, seconds, and milliseconds.

    But really, if you don’t want the timezone adjustment use new Date(year, month, day)

    firstDay = new Date(2011 , 7 , 1).getDate(); // returns 1 (first day of this month)
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