set options timeZoneName is not working

[ebsi-lruiz]

Hello,
I'm trying to use the options to set the timeZoneName so the string comes formatted using that time zone

I have something like this

const config = {  year: 'numeric',  month: 'short',  day: 'numeric',  timeZoneName: 'UTC', }
const formatter = new DateTimeFormat("en", config)
const result = formatter.format(new Date("2020-01-01")) 

the result should be Jan 1, 2020, but the timeZoneName is being ignored, I'm receiving Dec 31, 2019, instead

Looking at the code, I think I found a solution for that, it could be done in the formatNative function
something like this

// -- ios
...
const timeZone: NSTimeZone = getNativeTimeZone(timeZoneName);
        if (timeZone) {
            dateFormatter.timeZone = timeZone;
        }
...

// -- android
...
const timeZone: java.util.TimeZone = getNativeTimeZone(timeZoneName);
        if (timeZone) {
            sdf.setTimeZone(timeZone);
        }
...

Creating the corresponding getNativeTimeZone methods

If you'd like I can make the pull request

[CatchABus]

@lruiz-empyrean Does this return correct datetime for any given timezone?

[ebsi-lruiz]

@lruiz-empyrean Does this return correct datetime for any given timezone?

The current version doesn't, but changing the timezone before formatting it would, as long as you use the time zone IDs, such as: "UTC", "America/Argentina/Buenos_Aires", "America/Aruba", "America/Chicago", etc.

Reference:
https://developer.apple.com/documentation/foundation/nstimezone
https://developer.android.com/reference/java/util/TimeZone

Example:
format: 'YYYY-MM-dd HH:mm'
sourceDate: '2020-01-01'
config: { timeZoneName: 'here goes your target timezone id' }
formatter = new DateTimeFormat("en", config, format)

// 'UTC'
result = '2020-01-01 00:00'

// 'America/Argentina/Buenos_Aires'
result = 2020-12-31 21:00

// 'America/Aruba'
result = '2020-12-31 20:00'

// 'America/Chicago'
result = '2020-12-31 18:00'

[CatchABus]

I see. Could you provide your native example please?
I used the following code on android but no matter what timezone I set, it applies device zone on date.

const isoFormat = new java.text.SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss");
isoFormat.setTimeZone(java.util.TimeZone.getTimeZone("UTC"));
const date = isoFormat.parse("2010-05-23T09:01:02");
console.log(date);

EDITED: It seems device does not support 'UTC' :D
As long as zone exists on device, it works.

[ebsi-lruiz]

In the end, I've just inherited from the DatetimeFormat and overrode the current formatNative function in the library

 public formatNative(pattern: string, locale?: string, date?: Date): string {
        let sdf = locale ?
            new java.text.SimpleDateFormat(pattern, getNativeLocale(locale)) :
            new java.text.SimpleDateFormat(pattern);
        const timeZone: java.util.TimeZone = java.util.TimeZone.getTimeZone(this.options.timeZoneName);
        if (timeZone) {
            sdf.setTimeZone(timeZone);
        }
        return sdf.format(date ? new java.util.Date(date.valueOf()) : new java.util.Date()).toString();
    }

and then I used the new class the same as the original.

As long as zone exists on device, it works.

That's a good point to take into account.