服务器为UTC时区时，如何在JS中获取本地时区当日起止时间？

问题背景 #

服务器运行在UTC时区，需按Asia/Jakarta本地时区筛选数据，数据的collectTime为Unix时间戳。需要获取本地时区当日起止的Unix时间戳，但原有代码生成的结果与预期不符。

原有代码：

const { startOfDay, endOfDay, getTime, subDays } = require("date-fns");
const { utcToZonedTime } = require("date-fns-tz");

const timezone = "Asia/Jakarta";

const correctLocalStartDate = 1685379600000;
const correctLocalEndDate = 1685465999999;

const selectedUnixTime = subDays(new Date(), 1).getTime();

const localDate = utcToZonedTime(selectedUnixTime, timezone);

const localStartDate = getTime(startOfDay(localDate));
const localEndDate = getTime(endOfDay(localDate));

console.log(
  {
    isItCorrect: localStartDate === correctLocalStartDate,
    correctDate: new Date(correctLocalStartDate),
    systemDate: new Date(localStartDate),
  },
  "Start Date"
);

console.log(
  {
    isItCorrect: localEndDate === correctLocalEndDate,
    correctDate: new Date(correctLocalEndDate),
    systemDate: new Date(localEndDate),
  },
  "End Date"
);

运行结果：

{
  isItCorrect: false,
  correctDate: 2023-05-29T17:00:00.000Z,
  systemDate: 2023-05-30T07:00:00.000Z
} // Start Date

{
  isItCorrect: false,
  correctDate: 2023-05-30T16:59:59.999Z,
  systemDate: 2023-05-31T06:59:59.999Z
} // End Date

解决方法 #

问题出在基于UTC时间计算目标日期，导致本地时区的日期偏移。正确流程应基于本地时区计算日期，再转成UTC时间戳：

const { startOfDay, endOfDay, getTime, subDays } = require("date-fns");
const { utcToZonedTime, zonedTimeToUtc } = require("date-fns-tz");

const timezone = "Asia/Jakarta";

const correctLocalStartDate = 1685379600000; // 对应Jakarta时区2023-05-30 00:00:00
const correctLocalEndDate = 1685465999999;   // 对应Jakarta时区2023-05-30 23:59:59.999

// 1. 将当前UTC时间转成本地时区时间
const currentLocalTime = utcToZonedTime(new Date(), timezone);
// 2. 获取本地时区的前一天（按需调整，若要当天则去掉subDays）
const targetLocalDate = subDays(currentLocalTime, 1);

// 3. 获取本地时区当日的起止时刻（本地时间的00:00和23:59:59.999）
const localStart = startOfDay(targetLocalDate);
const localEnd = endOfDay(targetLocalDate);

// 4. 将本地时区的起止时刻转成UTC时间戳（Unix时间戳本质是UTC毫秒数）
const localStartDate = getTime(zonedTimeToUtc(localStart, timezone));
const localEndDate = getTime(zonedTimeToUtc(localEnd, timezone));

console.log(
  {
    isItCorrect: localStartDate === correctLocalStartDate,
    correctDate: new Date(correctLocalStartDate),
    systemDate: new Date(localStartDate),
    localStartDisplay: new Date(localStart).toLocaleString('en-US', { timeZone: timezone })
  },
  "Start Date"
);

console.log(
  {
    isItCorrect: localEndDate === correctLocalEndDate,
    correctDate: new Date(correctLocalEndDate),
    systemDate: new Date(localEndDate),
    localEndDisplay: new Date(localEnd).toLocaleString('en-US', { timeZone: timezone })
  },
  "End Date"
);

关键说明 #

• 先转本地时区再计算目标日期：确保基于本地时间逻辑获取“昨天/当天”，避免UTC时间带来的偏移
• 用zonedTimeToUtc转换起止时刻：Unix时间戳是UTC时间的毫秒数，需要把本地时区的起止时间转成对应的UTC时间再取戳

内容的提问来源于stack exchange，提问作者mandaputtra