Javascript getUTCDate return the previous day

Question

code like this

var date = new Date("2012/09/04");
console.log(date.getUTCDate());
//returns 3

can someone tell me how to get the correct date based on a time string like yyyy/mm/dd?

thx~

Answer 1

You shouldn't use getUTCxxx if you're dealing only with dates (i.e. you're not concerned about time). If you create a Date object like you did (specifying only the date) it will set the time to 0:00:00. When converting to UTC, if your timezone is positive it will subtract some time from your date, so your date will represent the previous day.

Instead, I'd suggest just using getDate for that.

Note: in my machine (I'm at UTC-3) the snippet above runs just fine (i.e. it returns 4), but that's because new Date("2012/09/04") here evaluates at:

alert(new Date("2012/09/04"));
// Tue Sep 04 2012 00:00:00 GMT-0300 (Hora oficial do Brasil)
alert(new Date("2012/09/04").toUTCString());
// Tue, 04 Sep 2012 03:00:00 GMT

If I were at, say, UTC+3 instead, I'd probably get results like:

alert(new Date("2012/09/04"));
// Tue Sep 04 2012 00:00:00 GMT+0300
alert(new Date("2012/09/04").toUTCString());
// Mon, 03 Sep 2012 21:00:00 GMT

Answer 2

Just tack on "UTC" to the end of your string when you pass it to the constructor:

function UTCDate(s) {
    return new Date(s + " UTC");
}