如何从Javascript获取DST的时区偏移量（不是客户端）？ [重复]

My website have 3 clocks (NYC, Tokyo, London).

And I hard-code the offset (-5, 9, 0):

$('#nyc-clock').clock({offset: '-5', type: 'analog'});
$('#tokyo-clock').clock({offset: '9',  type: 'analog'});
$('#london-clock').clock({offset: '0', type: 'analog'});

However, for New York, the timezone will be changed due to "Daylight saving time"

Can I have a function to get timezone offset? Like this:

get_timezone_offset("NewYork");

or:

is_dst();

Thank you.

Update:

Finally, I found the answer using php from the search engine. If you are using php => 5.3, you should scrolling down for the best answer.

And I really cannot find Javascript's method.

http://blog.mynzsky.com/?p=243

<?php
    function is_dst($where) {
        $timezone=date('e');
        date_default_timezone_set($where);
        $dst=date("I");
        date_default_timezone_set($timezone);
        return $dst;
    }   

    if (is_dst('America/New_York')) {
        $nyc_timezone = -4;
    } else {
        $nyc_timezone = -5;
    }
?>

</div>

If you like to calculate it in PHP the easiest is to set the default time zone to UTC and calculate from there, but it will work with PHP 5.2+

date_default_timezone_set('UTC');
echo timezone_offset_get(new DateTimeZone('Asia/Tokyo'),new DateTime('now'));

It will return the offset in seconds.

This will return correct offset even for DST.

in javascript like this

javascript:alert(new Date('2013/06/24').getTimezoneOffset())

Returns the time-zone offset from UTC