from `const now = new Date()`, how can I verify that I am before or equal a particular date at a given timezone and hour?

Question

I have a timezone map with publishing hour in the local zone with news that must define when they should be published on a date using a date picker.

This is a new news article that is initialized with the following:

{ timeZoneId: 'Europe/Paris, releaseHour: 9, publishingDateTime: undefined } // 9 is the hour GMT+1

I want to know how can I from const now = new Date(), verify if this article should be published today or the next day, the criteria are:

Is now before releaseHour? (is 9am GMT+1 in paris already passs or not)
If yes, then we should offer the next release slot at 9am GMT+1 + 1 day
If no, then we should use the release slot at 9am the same day

How is this possible?

This is how I have tried:

import { isBefore, isEqual } from 'date-fns';
import { utcToZonedTime } from 'date-fns-tz';

export const getNextPublishingDateTime = (now, timeZoneId, releaseHour) => {
  const zoned = utcToZonedTime(now, timeZoneId);
  const releaseTime = new Date(zoned.toISOString());
  releaseTime.setHours(releaseHour, 0, 0, 0);
  if (isBefore(zoned, releaseTime) || isEqual(zoned, releaseTime)) {
    console.log('before');
    return releaseTime;
  }
  releaseTime.setDate(releaseTime.getDate() + 1);
  console.log('after');
  return releaseTime;
};

But the hour returned by utcToZonedTime is not +01:00 offset, instead it is a date at my offset.

I have tried some other ideas, using moment-tz and vanilla Date, I found this task a bit complicated and hope to find help with the JS community as this look to be a normal date comparaison.

RobG · Answer 1 · 2020-03-22T15:35:59.407

You can use the Intl object and formatToParts method to get the current time in any supported timezone using IANA representative locations. It's reasonably well supported.

E.g.

function getHour(date, loc) {
  let d = new Intl.DateTimeFormat("en-EN", {
    hour: 'numeric',
    hour12: false,
    timeZone: loc
  });
  return d.formatToParts(date)[0].value;
}

let loc = 'Europe/Paris';
let now = new Date();
console.log(`The current hour in ${loc} is ${getHour(now, loc)}.`);

The above is just for illustration, there should be validation of input and return values.

from `const now = new Date()`, how can I verify that I am before or equal a particular date at a given timezone and hour?

1 Answers1