Spatial Exception

If you run into dates being a day early in ArcGIS javascript or other apps, here’s what’s happening I think ; )

FYI, UTC is for all practical purposes the same as GMT.

Esri recommends that databases are in UTC time. And if I’ve got this right, unless you set a time zone in your layer, you are entering a date in a date field as UTC. Mostly this is fine.You understand that the date refers to Pacific time for instance. You understand the date comes back to you the same value you put into the field. The problem comes when the browser or iOS or whatever device automatically localizes on initialization.

Problem: When ArcGIS Server returns a date, it sends milliseconds since epoch UTC (unix time). However, the Javascript Date object always creates a localized date when you use that to instantiate a Date object, e.g. Pacific Daylight Time, moving it back -7 hours. Thus, March 16 0:00am in the data becomes March 15 5:00pm — one day early.

A Solution: Keep everything in UTC. Use the javascript getUTC functions to return UTC time, which will match the stored date. (Yes, you could break this out into templates and formats, but really, how many different formats do you need for most apps.)

function getUTCDateYYYYMMDD(milliSecUnix) {
    var d, mm, dd;
    if (milliSecUnix) {
        d = new Date(milliSecUnix);
        mm = d.getUTCMonth() + 1;
        dd = d.getUTCDate();
        return (d.getUTCFullYear() + "-" +
                ((mm < 10) ? "0" + mm : mm) + "-" +
                ((dd < 10) ? "0" + dd : dd));
    }
    else {
        return "";
    }
}