仅计算一个特定时区的时区偏移量 [英] Calculate Timezone offset only for one particular timezone
问题描述
我正在尝试为一个在线教学并且位于德国的人构建一个应用程序.我想将该人的日程安排存储在一系列约会开始时间中.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(`${currentDate}T09:00:00Z`)
...
]
问题在于，在某些国家(例如德国)，存在斯坦达特(Standart)和夏令时.因此，在夏季，德国的出发时间为9:00、10:00和11:00，而在冬季，出发时间要早一小时.同时在一些国家(例如新加坡)，它们将保持不变:15:00、16:00、17:00 ...我该怎么办才能使德国的出发时间全年稳定并在其他地方改变分别:
The problem is that in some countries, like Germany, there are Standart and Summer times. So, while in summer the starting times in Germany would be 9:00, 10:00 and 11:00, in winter they would shift one hour earlier. At the same time in countries, like Singapore, they are gonna stay the same: 15:00, 16:00, 17:00... What do I have to do make the starting times in Germany stable throughout the year and change elsewhere respectively:
if (summerTimeInGermany) {
schedule = [
new Date(`${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
...
]
}
我需要此计划列表，以便将其与我从Google Calender获取的每日约会列表进行比较，并排除已经接受的约会.
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
我想您要尝试的是基于另一个时区中的时间戳并指定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.
一种实现方法是使用时间戳记作为UTC生成位置的日期，并查看小时和分钟的区别.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，应该会生成带有目标位置所需日期和时间的时间戳.
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代表位置来实现此算法.它只是经过轻微测试，因此请进一步测试.它会循环进行调整，以检查应用偏移量不会使日期在DST边界上移动，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，它会返回等效时间的ISO 8601 UTC时间戳，如果可选的 returnOffset 参数设置为true，它将改为返回偏移量.
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GMT东部和西部的标准和夏时制时间戳的示例(但不是很多).请进行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(/[\DT\s]/);
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>
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