将格式化的日期字符串更新为 UTC 值

Question

Users are able to submit only the date part of a date stamp eg 2020-12-01 , assuming that the time will be 00:00:00

So, if I have the above value, I want to update the time to its UTC value. So if I am in the EST timezone, I want to convert 2020-12-01 to 2020-12-01 05:00:00 to account for the five hour offset.

Can I do this with date-fns-tz ?

const { zonedTimeToUtc, format } = require("date-fns-tz");

const tz = Intl.DateTimeFormat().resolvedOptions().timeZone;

const utcDate = zonedTimeToUtc(new Date("2020-12-01"), tz);

document.getElementById("app").innerHTML = `${format(
  utcDate,
  "yyyy-MM-dd HH:mm:ss"
)}
`;

The above yields 2020-11-30 19:00:00 , which is moving the time 5 hours in the wrong direction.

https://codesandbox.io/s/happy-hoover-dn417?file=/src/index.js:23-301

Answer 1

Given:

const utcDate = zonedTimeToUtc(new Date("2020-12-01"), tz);

The built–in parser will be used to parse the string, so it will be parsed as UTC, then date-fns will apply the offset for the tz . Don't do that, use:

const utcDate = zonedTimeToUtc("2020-12-01", tz);

so that date-fns parses the string using the tz . Now utcDate.toISOString() produces "2020-12-01T05:00:00.000Z", which is the equivalent UTC date and time where tz is America/New_York.

Date-fns seems to always use the host timezone offset for output, the timeZone option just changes the text offset, it doesn't modify the actual timestamp values. Likely you have to use utcToZonedTime first to adjust the Date. I struggle with date-fns, I find the documentation seriously lacking in useful examples.

I'd just use toISOString and remove the "T" and "Z".