js获得当前时区夏令时发生和终止的时间代码

复制代码代码如下:
<！DOCTYPE html>
<html>
<head>
<title>DST Calculator</title>
<script type="text/javascript">

function DisplayDstSwitchDates（）
{
var year = new Date（）.getYear（）;
if （year < 1000）
year += 1900;

var firstSwitch = 0;
var secondSwitch = 0;
var lastOffset = 99;

// Loop through every month of the current year
for （i = 0; i < 12; i++）
{
// Fetch the timezone value for the month
var newDate = new Date（Date.UTC（year, i, 0, 0, 0, 0, 0））;
var tz = -1 * newDate.getTimezoneOffset（） / 60;

// Capture when a timzezone change occurs
if （tz > lastOffset）
firstSwitch = i-1;
else if （tz < lastOffset）
secondSwitch = i-1;

lastOffset = tz;
}

// Go figure out date/time occurences a minute before
// a DST adjustment occurs
var secondDstDate = FindDstSwitchDate（year, secondSwitch）;
var firstDstDate = FindDstSwitchDate（year, firstSwitch）;

if （firstDstDate == null && secondDstDate == null）
return "Daylight Savings is not observed in your timezone.";
else
return "Last minute before DST change occurs in " +
year + ": " + firstDstDate + " and " + secondDstDate;
}

function FindDstSwitchDate（year, month）
{
// Set the starting date
var baseDate = new Date（Date.UTC（year, month, 0, 0, 0, 0, 0））;
var changeDay = 0;
var changeMinute = -1;
var baseOffset = -1 * baseDate.getTimezoneOffset（） / 60;
var dstDate;

// Loop to find the exact day a timezone adjust occurs
for （day = 0; day < 50; day++）
{
var tmpDate = new Date（Date.UTC（year, month, day, 0, 0, 0, 0））;
var tmpOffset = -1 * tmpDate.getTimezoneOffset（） / 60;

// Check if the timezone changed from one day to the next
if （tmpOffset ！= baseOffset）
{
var minutes = 0;
changeDay = day;

// Back-up one day and grap the offset
tmpDate = new Date（Date.UTC（year, month, day-1, 0, 0, 0, 0））;
tmpOffset = -1 * tmpDate.getTimezoneOffset（） / 60;

// Count the minutes until a timezone chnage occurs
while （changeMinute == -1）
{
tmpDate = new Date（Date.UTC（year, month, day-1, 0, minutes, 0, 0））;
tmpOffset = -1 * tmpDate.getTimezoneOffset（） / 60;

// Determine the exact minute a timezone change
// occurs
if （tmpOffset ！= baseOffset）
{
// Back-up a minute to get the date/time just
// before a timezone change occurs
tmpOffset = new Date（Date.UTC（year, month,
day-1, 0, minutes-1, 0, 0））;
changeMinute = minutes;
break;
}
else
minutes++;
}

// Add a month （for display） since JavaScript counts
// months from 0 to 11
dstDate = tmpOffset.getMonth（） + 1;

// Pad the month as needed
if （dstDate < 10） dstDate = "0" + dstDate;

// Add the day and year
dstDate += "/" + tmpOffset.getDate（） + "/" + year + " ";

// Capture the time stamp
tmpDate = new Date（Date.UTC（year, month,
day-1, 0, minutes-1, 0, 0））;
dstDate += tmpDate.toTimeString（）.split（" "）[0];
return dstDate;
}
}
}

</script>
</head>
<body>
<script type="text/javascript">
document.write（"Current date/time: " + new Date（） + "<br />"）;
document.write（DisplayDstSwitchDates（））;
</script>
</body>
</html>