从JavaScript中的.NET DateTime JSON格式字符串获取正确的日期值

Question

I have a javascript application which receives data from ASP.NET WebService in JSON format. My application has a lot of manipulations with dates which it also receives from WebService.

WebService stores all dates in EST timezone and sends them in such format:

{"Date":"\/Date(1319205600000+0300)\/"} 

to my javascript application.

On the client side I should display all dates also in EST timezone irrespectively of browser's timezone. So if I receive from the server the representation of:

10/21/2011 10:00

I should display exactly the same time to the user.

So to convert dates I do something like this:

function convert_date(millisec) {
    var date = new Date(millisec),
        local_offset = date.getTimezoneOffset(),
        server_offset = -5 * 60, //EST offset
        diff = (local_offset + server_offset) * 60000;

    return new Date(millisec + diff);
}

But the point is that server_offset not always should be -5. It can be -4 depending on DST value. I've tried to do server_offset = (date.isDST() ? -4 : -5) * 60 instead but I haven't found any solution for capturing isDST() which works fine for all the local client timezones. Most of them work fine for that local browser's timezone which has the same value of DST as EST timezone but would fail in the case of GMT+5:30 timezone for example.

So are there any way to determine whether DST would be applied for some specific date in EST timezone from javascript?

Or maybe I've missed something?

Answer 1

If you can modify the web service, I would have it also return a flag indicating whether or not it was daylight saving time in the server's timezone (EST).

Assuming you can't do this, you can determine whether it is daylight saving time according to this information for DST in the United States :

DST starts on the second Sunday of March and it ends on the first Sunday of November.

The caveat being that this could change in the future (I wasn't even aware it had changed in 2007).

Answer 2

I am not really sure how exactly you are getting the ticks value you pass to the function, which I think you have something weird going on there. But if the question is how to write the isDST() function, then that should be pretty simple.

Date.prototype.isDST = function()
{
    var dt = new Date(this.getYear(), 1, 1);
    return dt.getTimezoneOffset() > this.getTimezoneOffset();
}

edit: This isn't polished/tested for negative offsets.