Elm Transit

elm package install etaque/elm-transit

Delayed actions with transition progress for enter/exit animations in Elm.

See also:

• elm-transit-router: a drop-in router with animated route transitions
• elm-transit-style: animations for elm-html style attribute

Usage

(Full working example here)

Use WithTransition record extension to extend your own model:

import Transit

type Msg =
  NavigateTo Page | SetPage Page | TransitMsg Transit.Msg

type Page =
  Page1 | Page2

-- notice `Msg` at end of type declaration
-- that's the type of the message to send during the transition
type alias Model =
  Transit.WithTransition { page: Page } Msg

You're not bound to root model, you can also use it for sub-pages or components transitions.

Then wrap Msg in one of your action types and call start and tick in your update function.

update : Msg -> Model -> (Model, Cmd Msg)
update action model =
  case action of

    NavigateTo page ->
      let
        timeline = Transit.timeline 100 (SetPage page) 200
        -- 100ms from 0 to 1, then action, then 200ms from 0 to 1
      in
        Transit.start TransitMsg timeline model

    TransitMsg a ->
      Transit.tick TransitMsg a model
        
    SetPage page ->
      ({ model | page = page }, Cmd.none)

A subscription is necessary to receive animation frame ticks when transition is running:

subscriptions : Model -> Sub Msg
subscriptions model =
  Transit.subscriptions TransitMsg model

In your views, you can then either:

• Use getValue to get the 1 -> 0 -> 1 varying Float, and getStep to know the current phase of transition.

• Or use one of the provided functions in elm-transit-style (or create one of your own) to add the visual effect in your view:

  div [ style (TransitStyle.fadeSlideLeft 50 model.transition) ] [ text "Some content" ]

Credits

• Thanks Alex Galays for the challenge