Question

In a previous question I wrote about a javascript date function that was mysteriously stopping on 11/07/101. Thanks to the stackoverflow users I was told my problem is Daylight Savings Time. Javascript date, is this my error or did I find a bug?

So my last question on this is what is the recommended approach in Javascript to deal with Daylight Savings Time?

Is http://code.google.com/p/datejs/ the best approach to solve this?

Answer 1

The best way is not to deal with DST. Use the UTC methods and you won’t have to worry about crossing a DST boundary, or any other timezone discontinuity (locale timezone rules can change for more reasons than just DST).

var timestamp= Date.UTC(2010, 10-1, 31, 0, 0, 0); // zero-based month: 9->october
var nextday= new Date(timestamp+86400000); // add one day
var ymd= [
    nextday.getUTCFullYear(),
    nextday.getUTCMonth()+1, // zero-based month
    nextday.getUTCDate()
].join('-');
alert(ymd); // 2010-11-1

If the above had been done with new Date(2010, ...) and getDate() etc, it’d return 2010-10-31, the day add failing due to the DST change (in my region, anyway).

It is a pity that the ‘default’ most-obvious methods in Date are about local time, especially since JavaScript provides so very little context to scripts on what ‘local time’ actually is. UTC is a more stable proposition.