Formatting of negative durations

[chrishens]

Hello,

I am trying to format a negative duration using Luxon. Specifically, I have a duration of -1.5 hours, and I would like to display it as -01:30. However, when I use the following code:

Duration.fromObject({ hours: -1.5 }).toFormat("hh:mm")

I get the output -01:-30 instead of the desired -01:30.

Could someone please help me understand how to correctly format a negative duration in this case (assuming this is possible)?

Thank you!

[dobon]

I have looked into this and agree that it is buggy behavior. I think we should patch this, but maybe that would be breaking for some people, so I'll leave that decision to leadership. I can't imagine how this behavior would be useful to anyone as-is.

It is not that pretty, but for practical purposes, you can suppress the negative sign using Intl.NumberFormat options, namely signDisplay, and then use additional logic to re-add the negative sign where you want it when applicable. eg:

const t = -1.5;
const signlessDuration = Duration.fromObject({ hours: t }).toFormat("hh:mm", {signDisplay: "never"});
return ((t < 0) ? "-" : "" ) + signlessDuration;

[diesieben07]

This is not necessarily desired for all durations. For example, -3 hours and 2 minutes might make people think the minutes are positive.
Therefor this will have to be behind an option, for example called leadingSignOnly.

Duration.fromObject({hours: -1.5}).toFormat('hh:mm'); // -01:-30 as before
Duration.fromObject({hours: -1.5}).toFormat('hh:mm', { leadingSignOnly: true }); // -01:30

What do you think?

[chrishens]

But isn't "T" already used as a formatting character for localized 24 hour time?

[diesieben07]

That's for DateTime.toFormat. Duration.toFormat uses a different set of tokens.

[chrishens]

I understand. I was just trying to avoid confusion. But following your logic you could opt for just using "T" for Duration.toFormat and omit the "hh:mm". This would then represent the duration as hh:mm in your desired locale with the appropriate "-" sign if the duration is negative. Just a thought.

[diesieben07]

Intl.DurationFormat is a very new API that has just arrived in browsers. Hence it is not supported by Luxon yet.
Luxon has Duration.toHuman which does something similar using Intl.NumberFormat.

I just looked at what Intl.DurationFormat does and it always only outputs a leading -, no matter the format. For example it will output '-1 hour, 30 minutes'.
With that, I think I have come around to changing toFormat to only adding a negative sign to the largest unit. A PR would be appreciated!

[dobon]

I've implemented a patch for this in a pull request: #1701

Any feedback or review is appreciated.