2016年7月 – 程序猿&程序媛

通过接口从后端获取时间戳，在前端用JS格式化显示。发现Chrome在Mac和Windows下，对特定的时间段（1986年至1991年），的处理方式并不相同。

//Mac下的Chrome浏览器
new Date(640450800000)
Thu Apr 19 1990 00:00:00 GMT+0900 (CDT)
new Date()
Mon Jul 04 2016 12:00:00 GMT+0800 (CST)
new Date(1467561600000)
Mon Jul 04 2016 00:00:00 GMT+0800 (CST)

//Windows下的Chrome浏览器
new Date(640450800000)
Wed Apr 18 1990 23:00:00 GMT+0800 (中国标准时间)
new Date()
Mon Jul 04 2016 12:00:00 GMT+0800 (中国标准时间)
new Date(1467561600000)
Mon Jul 04 2016 00:00:00 GMT+0800 (中国标准时间)

//Mac下的Chrome浏览器

new Date(640450800000)

Thu Apr 19 1990 00:00:00 GMT+0900 (CDT)

new Date()

Mon Jul 04 2016 12:00:00 GMT+0800 (CST)

new Date(1467561600000)

Mon Jul 04 2016 00:00:00 GMT+0800 (CST)

//Windows下的Chrome浏览器

new Date(640450800000)

Wed Apr 18 1990 23:00:00 GMT+0800 (中国标准时间)

new Date()

Mon Jul 04 2016 12:00:00 GMT+0800 (中国标准时间)

new Date(1467561600000)

Mon Jul 04 2016 00:00:00 GMT+0800 (中国标准时间)

查询资料后发现，原来中国也曾经使用过夏令时。

1986年至1991年，中华人民共和国在全国范围实行了六年夏令时，每年从4月中旬的第一个星期日2时整（北京时间）到9月中旬第一个星期日的凌晨2时整（北京夏令时）。除1986
年因是实行夏令时的第一年，从5月4日开始到9月14日结束外，其它年份均按规定的时段施行。1992年4月5日后不再实行。

要避免此情况可在后端对时间进行处理，返回格式化后的日期字符串。

TimeZone.setDefault(TimeZone.getTimeZone("GMT+8:00"));

1	TimeZone.setDefault(TimeZone.getTimeZone("GMT+8:00"));

或在前端通过getTimezoneOffset检测夏令时，尝试网上找到的夏令时检测算法。

<!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>

100

101

102

103

104

105

106

107

108

109

110

111

112

113

114

115

116

117

118

<!DOCTYPE html>

<html>

<head>

<title>DST Calculator</title>

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>

document.write("Current date/time: " + new Date() + "<br />");

document.write(DisplayDstSwitchDates());

</script>

</body>

</html>

参考资料：
时间是什么？
java中的时区陷阱
 Java —— 时区（夏令时）问题
 CST和GMT时间的区别
 使用 JavaScript 处理夏令时
 js获得当前时区夏令时发生和终止的时间
 List of time zone abbreviations
tz database
Daylight saving time
Time in China
Time zone
ISO 8601

月度归档： 2016年7月

Chrome在Mac和Windows下，对中国标准时间（CST）和中国夏令时(CDT)的不同处理。