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js獲得當前時區夏令時發生和終止的時間代碼

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js獲得當前時區夏令時發生和終止的時間代碼

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

代碼如下:

<!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> 

 

 

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