We will take a quick look at setting up the polyfill then see how you can use the Temporal API time zones. An example use case is to convert a meeting time from your local time zone for a colleague on another continent. No need to guess daylight saving adjustments any more!
There are a couple of polyfills suggested by TC39 for the Temporal API . We just take the first one here. Polyfills let you write code using new APIs before the APIs are widely supported. Behind the scenes, they convert your code (written using the new API) to widely supported code. This lets you get an early start on the the new API.
To get going install the polyfill package in your project:
That’s it. Next we see how you can do time conversion.
Let’s take a concrete use case. We are in London and have a friend in São Paulo. We want to call them now, but want to make sure it is a socially acceptable time for the call in São Paulo before dialling.
Lets start by setting up the local time zone. The Temporal API supports Time Zones using common time zone abbreviations (like CET for Central European Time, see IANA docs for more colour ) as well as city based ones. We will go for the latter:
Temporal.Now.plainDateTimeISO() gives us the current time. Because
we know we will be doing time zone conversion on it, we can use the
toZonedDateTime method to attach the local time zone to it. This is an exact point in time, meaning although it
is the clock time in London, it will not be the clock time in Berlin or Los Angeles.
Next we can set up our friend’s time zone:
this gives us a Time Zone object, for São Paulo, which we can use to translate time instants into São Paulo time:
Finally, you might want this in a human-readable format. You probably already know the date/month
order is reversed in some countries and can be a source of confusion. We can output our human
readable date using the
long style, which output text instead of numbers for months to help avoid a misunderstanding:
This outputs something like:
You can read more about Temporal API time zones in the TC39 Temporal.TimeZone docs
and Temporal Cookbook section on time zone conversion
. I am also collating a list of methods which I find useful into a cheatsheet. We’ll
have a quick look at that and then wrap up. Before that though, you can open up the code used to generate the example in StackBlitz
time conversion at the top of the
The Temporal API Cheatsheet is a quick reference learn in public list of Temporal methods. I am adding new methods to it as I discover more about the new API. It is open source and you can add to it yourself .
In this article, we have had a quick look at the Temporal API time zones functionality. In particular, we saw:
- how to create an exact time as a zoned date time in the Temporal API,
- a way to convert an instant from one time zone to another, like you would need to communicate an online meeting time to participants in different locations,
- how to output a date time in human readable format avoiding potential confusion from differing international conventions on month / date order.
You can see the code for the demo in the Rodney Lab GitHub repo .
I hope you found this article useful and am keen to hear how you will the starter on your own projects as well as possible improvements.
- Temporal.Instant is an exact time, but not related to a time zone. As an example a time given in Coordinated Universal Time (UTC). That instant uniquely identifies a a specific point of time, which will be different to wall clock time as you move around the globe. Meanwhile Temporal.PlainDateTime is wall clock time (e.g. the time a user’s computer shows). This will be a different instant in time in different time zones. That is because the instant when the computer says 10:00 in Sydney and Los Angeles are actually hours apart. Finally a ZonedDateTime is, in some ways like a Temporal.Instant, in that it uniquely identified a precise point in time. However it has a time zone attached, making it more useful from a human perspective. That’s because if you are in São Paulo it is more useful to know the time is 14:00 local time that 18:00 UTC.
- To convert an exact time between time zones in the Temporal API first create the local time as a PlainDateTime: `let local = Temporal.Now.plainDateTimeISO`. Then you can convert this to a zoned date time: `local.toZonedDateTime('Europe/London')`. Finally create a time zone object for the remote time zone and use that in withTimeZone(): `let remoteTZ = Temporal.TimeZone.from('America/Sao_Paulo');` `let remote = local.withTimeZone(remoteTZ);`.
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Just written a new article talking in a little more detail on what I have learned on converting from one time zone to another.— Rodney (@askRodney) May 13, 2022
There's also a link to an 🚀 Astro test repo for playing around with.
Hope you find it useful!
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