Javascript date, is this my error or did I find a bug?

Question

I have a section of simple Javascript in my application that has a link \"Add Day\", which adds 1 day to a date. It always works perfectly, except when the date gets to be

Answer 1

Others spotted what the problem is.

To fix it you can use the overloaded Date constructor that takes the year, month, and day:

var aDate = new Date(2010, 10, 07);
var aDatePlusOneDay = new Date(aDate.getFullYear(),
                               aDate.getMonth(),
                               aDate.getDate() + 1, // HERE
                               aDate.getHours(),
                               aDate.getMinutes(),
                               aDate.getSeconds(),
                               aDate.getMilliseconds()); 

Here's a more generic solution that can increment any date by a given millisecond amount, taking changes to daylight savings into account:

Date.addTicks = function(date, ticks) {
  var newDate = new Date(date.getTime() + ticks);
  var tzOffsetDelta = newDate.getTimezoneOffset() - date.getTimezoneOffset();
  return new Date(newDate.getTime() + tzOffsetDelta * 60000);
}

Adding a day to a Date object then is a matter of adding the number of milliseconds in one day:

Date.addTicks(new Date(2010, 10, 7), 86400000); // new Date(2010, 10, 8)

References:

• Date.prototype.getTimezoneOffset