仅计算一个特定时区的时区偏移 [英] Calculate Timezone offset only for one particular timezone
问题描述
我正在尝试为一位在德国进行在线教学的人开发一款应用.我想将人的日程安排存储在约会开始时间的数组中.例如:
I am trying to build an app for a person who is teaching online and is based in Germany. I want to store the person's schedule in an array of appointment starting times. For example:
let schedule = [
new Date(`${currentDate}T07:00:00Z`),
new Date(`${currentDate}T08:00:00Z`),
new Date(`${currentDate}T09:00:00Z`)
...
]
问题是在某些国家/地区，例如德国，有标准时间和夏令时.因此，在夏季，德国的出发时间是 9:00、10:00 和 11:00，而在冬季，它们会提前一小时.与此同时，在新加坡等国家，他们将保持不变:15:00、16:00、17:00……我必须做什么才能使德国的开始时间全年稳定，而在其他地方有所变化分别:
The problem is that in some countries, like Germany, there are Standart and Summer times. So, while in summer the starting times in Germany would be 9:00, 10:00 and 11:00, in winter they would shift one hour earlier. At the same time in countries, like Singapore, they are gonna stay the same: 15:00, 16:00, 17:00... What do I have to do make the starting times in Germany stable throughout the year and change elsewhere respectively:
if (summerTimeInGermany) {
schedule = [
new Date(`${currentDate}T07:00:00Z`), // 9:00 in Germany
new Date(`${currentDate}T08:00:00Z`), // 10:00
new Date(`${currentDate}T09:00:00Z`) // 11:00
...
]
} else {
schedule = [
new Date(`${currentDate}T08:00:00Z`), // 9:00
new Date(`${currentDate}T09:00:00Z`), // 10:00
new Date(`${currentDate}T10:00:00Z`) // 11:00
...
]
}
我需要这个日程表，这样我就可以将它与我从 Google 日历获取的每天约会列表进行比较，并排除已经预约的约会.
I need this schedule list so that I could compare it with the list of appointments per day, which I fetch from Google Calender, and exclude the ones that are already taken.
推荐答案
我认为您想要做的是根据另一个时区的时间戳并给定 IANA 代表位置来生成 UTC 时间戳.
What I think you're trying to do is to generate a UTC timestamp based on a timestamp in another timezone and given the IANA representative location.
这样做的一种方法是使用时间戳作为 UTC 生成位置的日期，并查看小时和分钟的差异.那应该是偏移量.然后将偏移量应用于原始时间戳.然后，当应用时区偏移时，应该会生成一个时间戳，其中包含目标位置所需的日期和时间.
One way of doing that is to generate a Date for the location using the timestamp as UTC and see what the difference in hours and minutes are. That should be the offset. Then apply the offset to the original timestamp. That should then generate a timestamp with the required date and time for the target location when the timezone offset is applied.
以下函数使用 Intl.DateTimeFormat 和 IANA 代表位置实现此算法.它只是经过轻微测试，所以请进一步测试.它为调整执行循环以检查应用偏移量不会将日期移动到 DST 边界上，因此需要重新调整偏移量.
The following function implements this algorithm using Intl.DateTimeFormat and IANA representative location. It's only been lightly tested so please test further. It does a loop for the adjustments to check that applying the offset doesn't move the date over a DST boundary and hence needs to readjust the offset.
默认情况下，它返回等效时间的 ISO 8601 UTC 时间戳，如果可选的 returnOffset 参数设置为 true，则返回偏移量.
By default it returns an ISO 8601 UTC timestamp for the equivalent time, if the optional returnOffset parameter is set to true, it returns the offset instead.
我提供了格林威治标准时间东部和西部的标准和夏令时时间戳示例(但不是很多).请彻底测试并根据需要进行修改.
I've provided examples of standard and daylight saving timestamps both east and west of GMT (but not many). Please test thoroughly and modify as required.
/* @param {string} isoString - ISO 8601 timestamp without timezone
** e.g. YYYY-MM-DDTHH:mm:ss or YYYY-MM-DD HH:mm:ss
** @param {string} loc - IANA representateive location
** e.g. Europe/Berlin
** @param {boolean} returnOffset - if true, return the offset instead of timestamp
** @returns {string} if returnOffset is true, offset is ±HH:mm[:ss] (seconds only if not zero)
** if returnOffset is false, equivalent ISO 8601 UTC timestamp
*/
let getUTCTime = (function() {
let n = 'numeric';
let formatterOpts = {year:n, month:n, day:n, hour:n, minute:n, second:n, hour12: false};
// Parse YYYY-MM-DDTHH:mm:ss as UTC (T can be space)
function parse (isoString) {
let [Y,M,D,H,m,s] = isoString.split(/[DTs]/);
return new Date(Date.UTC(Y,M-1,D,H,m,s));
}
// Get date parts, use supplied formatter
function toParts(date, formatter) {
return formatter.formatToParts(date).reduce((acc, part) => {
acc[part.type] = part.value;
return acc;
}, Object.create(null));
}
return function (isoString, loc, returnOffset = false) {
// Update formatter options with loc so get target loc values
formatterOpts.timeZone = loc;
// Formatter
let formatter = new Intl.DateTimeFormat('en', formatterOpts);
// Parse input string as UTC
let oDate = parse(isoString);
// Date to adjust to wanted values
let utcDate = new Date(oDate);
// maxLoops limits do..while in dilemma zone, ensures sensible value
let maxLoops = 3,
p, diff;
// Adjust utcDate so it generates required local date values
// Adjustment may shift over DST boundary so may need 2nd adjustment
// Limit number of loops (shouldn't be required but just in case...)
do {
// Get date parts in target timezone
p = toParts(utcDate, formatter);
// Get difference between local and adjusted values
diff = new Date(Date.UTC(p.year, p.month-1, p.day, p.hour, p.minute, p.second)) - oDate;
// If necessary, adjust utcDate so it generates required values when shifted
if (diff) {
utcDate.setTime(utcDate.getTime() - diff);
}
// Loop until generated values match original or maxLoops
} while (diff && maxLoops--)
// If maxLoops is -1, hit DST dilemma zone: time doesn't exist on that date
// E.g. going into daylight saving at 02:00, then 02:30 doesn't exist
// and loop will flip in/out of DST until stopped by maxLoops
// So generate valid date and offset in DST period
let dDiff = null;
if (maxLoops < 0) {
p = toParts(utcDate, formatter);
dDiff = Date.UTC(p.year, p.month - 1, p.day, p.hour, p.minute, p.second) - utcDate;
let msg = isoString + ' does not exist at ' + loc + ' due to ' +
'daylight saving change-over, shifting into DST';
// console.log(msg);
// throw new RangeError(msg);
}
// Convert diff between local and adjusted to get ±HH:mm offset
// Use dilemma diff (dDiff) if has been set
let oDiff = dDiff || oDate - utcDate;
let sign = oDiff > 0? '+' : '-';
oDiff = Math.abs(oDiff);
// console.log(sign + new Date(oDiff).toISOString().substring(11,19).replace(/:00$/,''));
let offH = oDiff / 3.6e6 | 0;
let offM = (oDiff % 3.6e6) / 6e4 | 0;
let offS = (oDiff % 6e4) / 1e3 | 0;
let z = n=>(n<10?'0':'')+n;
// Return offset (with offset seconds if not zero) or ISO 8601 UTC string
return returnOffset? `${sign}${z(offH)}:${z(offM)}${offS? ':' + z(offS) : ''}` :
utcDate.toISOString();
}
})();
// Given a local timestmap in format YYYY-MM-DDTHH:mm:ss and
// loc as IANA representative location
// Return equivalent ISO 8061 UTC timestmap
function getUTCString(timestamp, loc) {
return getUTCTime(timestamp, loc);
}
// Given a local timestmap in format YYYY-MM-DDTHH:mm:ss and
// loc as IANA representative location
// Return offset at loc as ±HH:mm[:ss]
// - seconds only included if not zero (typically pre-1900)
function getUTCOffset(timestamp, loc) {
return getUTCTime(timestamp, loc, true);
}
// Examples
window.onload = function() {
let t = document.getElementById('t0');
let params = ['Local time', 'UTC time', false];
let showData = (localTime, loc, offset, timeUTC) => {
let row = t.insertRow();
[localTime, loc, timeUTC, null, null].forEach((s, i) => {
cell = row.insertCell();
cell.textContent = i == 0? localTime.replace('T',' '):
i == 1? loc:
i == 2? offset :
i == 3? timeUTC :
new Date(timeUTC).toLocaleString('en-CA', {timeZone: loc, hour12: false}).replace(',','') ;
});
return new Date(timeUTC).toLocaleString('en-CA', {timeZone: loc, hour12: false}).replace(',','');
};
// Local time required Location
[['2020-04-22T09:00:00','Europe/Berlin'], // DST offset +2
['2020-01-22T09:00:00','Europe/Berlin'], // Std offset +1
['2020-04-22T09:00:00','America/Denver'], // DST offset -6
['2020-01-22T09:00:00','America/Denver'], // Std offset -7
['2020-04-22T09:00:00','US/Aleutian'], // DST offset -9
['2020-01-22T09:00:00','US/Aleutian'], // Std offset -10
['2020-01-22T09:00:00','Pacific/Honolulu'],// Std offset -11
['2020-01-22T19:00:00','Pacific/Honolulu'],// Std offset -11
['2020-04-22T09:00:00','Asia/Singapore'], // Std offset +8
['2020-04-22T09:00:00','Pacific/Apia'], // Std offset +13
['2020-01-22T09:00:00','Pacific/Apia'], // DST offset +14
['2020-01-22T09:00:00','Asia/Yangon'], // Std offset +6:30
['2020-04-22T09:00:00','Pacific/Chatham'], // Std offset +12:45
['2020-01-22T09:00:00','Pacific/Chatham'], // DST offset +13:45
// Historic offsets pre 1900
['1857-01-01T00:00:00','Europe/Berlin'], // Std offset +00:53:28
['1857-01-01T00:00:00','Australia/Sydney'],// Std offset +10:04:52
['1857-01-01T00:00:00','America/New_York'],// Std offset -04:56:02
['1857-01-01T00:00:00','America/Sao_Paulo'],//Std offset -03:06:28
// DST boundary check out of DST (2 to 3 am counted as "out")
['2020-04-05T01:45:00','Australia/Sydney'],// DST offset +11:00
['2020-04-05T01:59:59','Australia/Sydney'],// DST offset +11:00
['2020-04-05T02:00:00','Australia/Sydney'],// Std offset +10:00
['2020-04-05T02:30:00','Australia/Sydney'],// Std offset +10:00
['2020-04-05T03:00:00','Australia/Sydney'],// Std offset +10:00
['2020-04-05T03:15:00','Australia/Sydney'],// Std offset +10:00
// DST boundary check into DST (2 to 3 am counted as "in")
['2020-10-04T01:45:00','Australia/Sydney'],// Std offset +10:00
['2020-10-04T02:00:00','Australia/Sydney'],// DST offset +11:00
['2020-10-04T02:30:00','Australia/Sydney'],// DST offset +11:00
['2020-10-04T02:59:59','Australia/Sydney'],// DST offset +11:00
['2020-10-04T03:00:00','Australia/Sydney'],// DST offset +11:00
['2020-10-04T03:15:00','Australia/Sydney'] // DST offset +11:00
].forEach(([localTime,loc]) => {
// Show results
let timeUTC = getUTCString(localTime, loc);
let offset = getUTCOffset(localTime, loc);
showData(localTime, loc, offset, timeUTC);
});
};
// Example use
let timestamp = '2020-06-30 08:30:00';
let locBer = 'Europe/Berlin';
let locSng = 'Asia/Singapore';
// Get UTC timestamp and offset for Berlin
let utc = getUTCString(timestamp, locBer);
let off = getUTCOffset(timestamp, locBer);
// Show times and offset - offset is just for display, not used to
// generate Singapore timestamp
console.log('Berlin : ' + timestamp + ' ' + off); //
console.log('Singapore: ' + new Date(utc).toLocaleString(
'en-CA',{hour12:false, timeZone:locSng, timeZoneName:'short'}
).replace(',',''));table {
border-collapse: collapse;
}
td {
font-family: geneva, arial;
font-size: 80%;
padding: 5px;
border: 1px solid #bbbbbb;
}
td:nth-child(2) {
font-family: monospace;
font-size: 100%;
}<table id="t0">
<tr><th>Local time<th>Place<th>Offset<th>UTC<th>Check
</table>这篇关于仅计算一个特定时区的时区偏移的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
