检查夏令时 [英] Checking for daylight saving

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本文介绍了检查夏令时的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！

问题描述

我正在研究一个功能，以确定在特定日期是否观察到夏令时

（考虑到平台的区域

设置）并且遇到了建议在merlyn.com上测试时间

各个日期的区域偏移，看它是否有变化。基于

，我开发了以下checkDST（）函数，据我所知
可以说，应该足够了。

它会检查传递给它的日期或当前日期，其他日期为3

，将来每3个月一次。如果他们的

时区中的任何一个时区与时期不同，那么：

true - 在日期观察到夏令时，或

false - 观察到夏令时但不是日期

返回
。如果没有找到差异，则返回undefined。我将
明确地返回undefined作为样式而不是让

循环切断并默认返回undefined。

任何人都可以建议算法是否合适，如果我的

实现是否正常？如果时区发生变化，则会失败

与夏令时无关的偏移量，如果发生变化，则b / b
的期限少于3个月且在测试的日期。

据我所知，没有任何地方能做到这一点，但他们可能会被可接受的纳入b $ b范围"测试（比如允许更改

到5分钟）并检查对称性 - 如果时区是x / b $ b不同的x个月时间，检查它是否也不同（ 12 - x）

个月前，检查是否有相同的金额考虑到

考虑可接受的范围。

function checkDST（ d）{

d = d || new Date（）;

var x = new Date（d）;

var dt = d.getTimezoneOffset（）;

var xt;

for（var i = 0; i< 3; i ++）{

x.setMonth（x.getMonth（）+ 3）

xt = x.getTimezoneOffset（）;

if（dt！= xt）{

return dt< xt;

}

}

返回undefined;

}

function showDST（）{

var x = isDST（new Date（））;

var msg;

if（x === true）{

msg =''在这里观察夏令时''+

''并且有效。'';

}否则如果（x === false）{

msg =''在这里观察到夏令时'''

''但不是现在。'';

}否则{

msg =''这里根本没有观察到夏令时。''

}

alert（x +''：''+ msg）;

}

showDST（）;

-

Rob

I was investigating a function to determine whether daylight saving
was being observed on a particular date (given the platform''s regional
settings) and came across a suggestion at merlyn.com to test the time
zone offset on a variety of dates to see if it changes. Based on
that, I developed the following checkDST() function which, as far as I
can tell, should be sufficient.

It checks either the date passed to it or the current date with 3
other dates, each 3 months further into the future. If any of their
time zones differs from the epoch then either:

true - daylight saving is being observed on the date, or

false - daylight saving is observed but not on the date

are returned. If no difference is found, undefined is returned. I
explicitly return undefined as a matter of style rather than let the
loop peter out and return undefined by default.

Can anyone suggest whether the algorithm is appropriate and if my
implementation is OK? It will fail if there are changes to time zone
offsets that are not related to daylight saving, and if changes occur
for a period of less than 3 months and fall within the dates tested.

As far as I know, there isn''t anywhere that does that, but they might
be accommodated by an "acceptable range" test (say allow changes of up
to 5 minutes) and checking for symmetry - if the time zone is
different in x months time, check if it was also different (12 - x)
months ago, and check if it differed by the same amount taking into
consideration the acceptable range.
function checkDST(d) {

d = d || new Date();

var x = new Date(d);
var dt = d.getTimezoneOffset();
var xt;

for (var i=0; i<3; i++) {
x.setMonth(x.getMonth() + 3)
xt = x.getTimezoneOffset();

if (dt != xt) {
return dt < xt;
}
}
return undefined;
}

function showDST(){

var x = isDST(new Date());
var msg;

if (x === true) {
msg = ''Daylight saving is observed here '' +
''and is in force.'';
} else if (x === false) {
msg = ''Daylight saving is observed here, '' +
''but not at the moment.'';
} else {
msg = ''Daylight saving is not observed here at all.''
}
alert(x + '': '' + msg);
}

showDST();

--
Rob

检查夏令时 [英] Checking for daylight saving

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