Provide support for specific events

[kladdad]

Consider the following code, where I am trying to get the value of a text field in response to a change event.

    def setCity(event: Event): Unit = {
      val value = event.target.asInstanceOf[HTMLInputElement].value
      setState(state.copy(city = value))
    }

It would be nice to be able to specify a more specific event type instead of Event in onChange to avoid the asInstanceOf[HTMLInputElement] part.