Elm Language The Elm Architecture Program with Flags
Example
programWithFlags has only one difference from program.
It can accept the data upon initialization from JavaScript:
var root = document.body;
var user = { id: 1, name: "Bob" };
var app = Elm.Main.embed( root, user );
The data, passed from JavaScript is called Flags.
In this example we are passing a JavaScript Object to Elm with user information, it is a good practice to specify a Type Alias for flags.
type alias Flags =
{ id: Int
, name: String
}
Flags are passed to the init function, producing the initial state:
init : Flags -> ( Model, Cmd Msg )
init flags =
let
{ id, name } =
flags
in
( Model id name, Cmd.none )
You might notice the difference from it's type signature:
programWithFlags :
{ init : flags -> ( model, Cmd msg ) -- init now accepts flags
, update : msg -> model -> ( model, Cmd msg )
, subscriptions : model -> Sub msg
, view : model -> Html msg
}
-> Program flags
The initialization code looks almost the same, since it's only init function that is different.
main =
programWithFlags
{ init = init
, update = update
, view = view
, subscriptions = subscriptions
}
