How to validate a date?

Question

I\'m trying to test to make sure a date is valid in the sense that if someone enters 2/30/2011 then it should be wrong.

How can I do this with any date?

Answer 1

This solution does not address obvious date validations such as making sure date parts are integers or that date parts comply with obvious validation checks such as the day being greater than 0 and less than 32. This solution assumes that you already have all three date parts (year, month, day) and that each already passes obvious validations. Given these assumptions this method should work for simply checking if the date exists.

For example February 29, 2009 is not a real date but February 29, 2008 is. When you create a new Date object such as February 29, 2009 look what happens (Remember that months start at zero in JavaScript):

console.log(new Date(2009, 1, 29));

The above line outputs: Sun Mar 01 2009 00:00:00 GMT-0800 (PST)

Notice how the date simply gets rolled to the first day of the next month. Assuming you have the other, obvious validations in place, this information can be used to determine if a date is real with the following function (This function allows for non-zero based months for a more convenient input):

var isActualDate = function (month, day, year) {
    var tempDate = new Date(year, --month, day);
    return month === tempDate.getMonth();
};

This isn't a complete solution and doesn't take i18n into account but it could be made more robust.