Add to handle events thrown by custom components.

[chexxor]

I think Pux needs an evt function to allow users to respond to events containing arbitrarily-shaped data, as third-party components often fire uniquely-shaped events. This is similar to the attr function, which already exists in this library. What do you think?

Details of my use-case follows.

I imported the React Bootstrap Datepicker components into my project, using the Pux.fromReact function, and I want to respond to the onChange event it fires. The type of the event it throws is unlike any event defined in this repo, it is type DatePickerSelectEvent = String, where the String is the ISO-encoded date which was selected.

Here's the relevant snippets from my project, which might clarify.

import App.ReactBootstrap.Components as RBC
...
type DatePickerSelectEvent = String
data Action = x | y | ChangeReservationDate DatePickerSelectEvent
...
update (ChangeReservationDate newDate) state = noEffects $ state { reservationDate = newDate }
...
view state =
  form [ onSubmit (ReservationViewChange) ]
    [ formGroup [ attr "controlId" "reservationDate" ]
      [ controlLabel []
        [ text "Reservation Date" ]
      , RBC.datePicker [ attr "id" "reservation-datepicker",  value state.reservationDate, evt "onChange" ChangeReservationDate ]
        []
      ]
    , ...

[alexmingoia]

Released in Pux 7.2