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js獲得當(dāng)前時區(qū)夏令時發(fā)生和終止的時間代碼

更新時間：2014年02月23日 16:00:09 作者：

這篇文章主要介紹了js獲得當(dāng)前時區(qū)夏令時發(fā)生和終止的時間代碼,需要的朋友可以參考下

 
<!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> 

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