.format adds 1 hour to time I pass it

[danielmsrodrigues]

I'm using node js and am trying to make a reservation system.
I'm using prisma to work on my database and prisma's default datetime format is YYYY-MM-DDTHH:mm:ss.000Z.

I'm passing the datetime as 2023-06-06T12:00:00.000Z and it is being stored correctly on my database. However, I'm trying to send confirmation and cancelation emails to each user creating or removing a reservation and I don't want to send an email saying "Reservation for 2023-06-06T12:00:00.000Z confirmed".
For that reason, I tried using date-fns and created a variable:

import { format } from "date-fns"

const formattedReservationHour = format(
  new Date(reservation_hour),
  "HH:mm"
);

When I console log this formattedReservationHour or received the email, for some reason date-fns is adding 1 hour to the time I pass it (instead of 12:00, it turns into 13:00). How can I fix this?

Please let me know if you can help in some way.

[nyalsadiq]

I appreciate this was asked a while ago but I got tripped up by this recently. The format function seems to output using the timezone of the runtime device. So for example, if you are in British Summer Time (UTC+1) and pass new Date('2023-06-06T12:00:00.000Z') into format, you'll get out a timestamp that is one hour ahead - 2023-06-06T13:00:00.000Z. I'm sure there's an interesting reason for this but I've not taken the time to look into it.

To force date-fns to stick to UTC and not perform this conversion we need to use a date object from date-fns/utc. Example:

import { UTCDateMini } from '@date-fns/utc';
import { format } from 'date-fns/format';

const veryGoodFunctionName = (date: Date): string => format(new UTCDateMini(date), "HH:mm");