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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>javascript排行
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