date - 如何在 Elm 中以格林威治标准时间显示当前时区偏移量

Question

I'm stuck on getting the current Timezone offset from the Date in Elm.

Date.now

This returns <Thu Feb 22 2018 20:42:42 GMT+0530 (India Standard Time)> as string As I have explored in Elm's core lib of date and time, and they don't provide any direct method to fetch the current timezone offset. So what should I do?

import Html as App
import Html exposing (..)
import Date exposing (Date)
import Task


type alias Model = 
  Maybe Date


type Msg = 
  SetDate (Maybe Date)


update : Msg -> Model -> (Model, Cmd Msg)
update (SetDate date) _ = 
  (date, Cmd.none)


view : Model -> Html Msg
view model =
  div [] [ text <| dateString model ]


dateString : Model -> String
dateString model =
  case model of
    Nothing -> "No date here"
    Just date ->
      (toString <| date)

now : Cmd Msg
now = 
  Task.perform (Just >> SetDate) Date.now




main : Program Never Model Msg
main =
  App.program 
    { init = ( Nothing, now ) 
    , view = view
    , subscriptions = always Sub.none 
    , update = update
    }

I need this +0530 as in the float 5.5.

Answer 1

Elm 的 DateTime 函数目前非常稀疏，但 justinmimbs Date.Extra 库是我解决此类问题的首选。看看 here

你可以这样导入，

import Date.Extra exposing (offsetFromUtc)

然后，你在哪里 toString <| date将您的管道更改为

date
    |> offsetFromUtc
    |> toString

这将在几分钟内为您提供偏移量，如果您想要浮点值，只需将 int 除以 60。这里的简单函数是:

divBy60 : Int -> Float
divBy60 t =
    toFloat t / 60.0

然后只需再次将您的管道更改为

date
    |> offsetFromUtc
    |> divBy60
    |> toString