Elm onSelect decoder

onSelect.elm

-- Assuming we have a list of items in the model (type alias Model = { items : List Item }
-- where Item is a record like { id : Int, name : String }

-- this goes in the view and generates an html dropdown
select
   [ onSelect ValueSelectedMsg ]
   (List.map (\item -> option [ value (toString item.id) ] [ text item.name ]) model.items)


targetSelectedIndex : Json.Decoder Int
targetSelectedIndex =
    Json.at [ "target", "selectedIndex" ] Json.int


onSelect : (Int -> msg) -> Html.Attribute msg
onSelect msg =
    on "change" (Json.map msg targetSelectedIndex)

-- This will send a message containing the selected index (eg. ValueSelectedMsg 1)

Thanks for this.
Got here from this SO answer