JS: parse time to pull out hours and minutes using date-fns, ignroing timezones

Question

My backend sends me a timestamp in the following format: 2019-12-15T20:00:00.000Z which is UTC time. Now all I need is to pull out the time without modifying it for timezones. I am using date-fns but every time I try to get the time I either get an Invalid Date or it modifies the time to the local timezone. Right now my code is:

import { format, parse, parseISO } from 'date-fns'

format(parseISO('2019-12-15T20:00:00.000Z'), 'h:mm a')

What I want is: 8:00 PM but what I get is 3:00 PM because its converting from UTC to EST time (my local timezone). I know I can do things like to IsoString and then parse the string, but I am looking for a way to use date-fns to do it so I don't have to write custom string parsers. There has to be an easy way to just ignore timezones?

Does this answer your question? [date-fns | How do I format to UTC](https://stackoverflow.com/questions/58561169/date-fns-how-do-i-format-to-utc) — iPhoenix, Dec 15 '19 at 17:35
@iPhoenix Not really. That answers how to get a Date object into an ISO string and then perform calculations on the string. In my question my date/timestamp is already in an ISO string. What I am looking for is to use date-fns for easy formatting of that string. I can parse the ISO string also, but it just seems hackish if I am using date-fns. — Darkisa, Dec 15 '19 at 17:42
I am. I am doing something similar now where I remove the timezone using vanilla JS and then using that string, I do my date operations, but I figured I try to see if there are better solutions. — Darkisa, Dec 15 '19 at 17:46

score 2 · Answer 1 · answered Dec 15 '19 at 17:55

I am going to answer my own question with how I make it work in case it helps someone, but I am still looking to see if there is a better alternative of just using date-fns since mine seems a bit hackish:

What I do is remove the timezone from the ISO string and then use that time with date-fns:

let time = "2019-12-15T20:00:00.000Z".slice(0, -5)

The above is a time with no time zone, and because there is no timezone date-fns assumes the local timezone, so when you do:

format(parseISO(time), 'h:mm a')

you get: 8:00 PM, or whatever format you prefer. You just have to be careful with the string that you are slicing. If its always the same format then it should work.

Thanks! This is super helpful to know that parseISO will prevent adding timezone information! — Igor Soloydenko, Jul 27 '20 at 06:52

score 0 · Answer 2 · answered Dec 15 '19 at 18:01

Here is one solution that manually formats the string using the vanilla JS Date object:


const date = new Date('2019-12-15T20:00:00.000Z');

function format(date) {
  const hours = date.getUTCHours();
  const minutes = date.getMinutes();

  return (1 + ((hours - 1) % 12)) + ":" + minutes.toString().padStart(2, "0") + " " + ((hours > 11) ? "PM" : "AM");
}

format(date);

JS: parse time to pull out hours and minutes using date-fns, ignroing timezones

2 Answers2