Time in

About Time

The Time module is used to display human-readable dates / times. While it's technically possibly to manipulate times with Time, there are Elm community packages that are far more suited to the task, such as justinmimbs/date or CoderDennis/elm-time-format.

Posix

Times are represented by the opaque type Posix, which wraps Unix epoch time, the number of milliseconds passed since January 1st, 1970 at midnight UTC. A Posix is an non-ambiguous value that does not vary between time zones, therefore a good choice for keeping time. In an Elm application, Posix times will typically be provided by external sources, such as the browser.

It is possible to transform a Posix into a number of millisecond and vice-versa with the following functions:

posixToMillis : Posix -> Int
millisToPosix : Int -> Posix

Time Zones

In our day-to-day lives, we humans usually don't read Posix and instead prefer local time, which depends on our location on Earth, and local daylight-saving rules. In Elm, this information is encoded in the opaque type Zone, usually provided by the browser.

There is a special Zone that is always accessible:

utc : Zone

Human times

With a Posix and a Zone, we have enough information to show local time in any level of details. Here is a list of the functions that can be used for that:

toYear : Zone -> Posix -> Int
toMonth : Zone -> Posix -> Month
toDay : Zone -> Posix -> Int
toWeekday : Zone -> Posix -> Weekday
toHour : Zone -> Posix -> Int
toMinute : Zone -> Posix -> Int
toSecond : Zone -> Posix -> Int
toMillis : Zone -> Posix -> Int

You will have spotted two more Time custom types:

type Month = Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec
type Weekday = Mon | Tue | Wed | Thu | Fri | Sat | Sun

It is left to users to convert these custom types to human-readable values.