js/_of_ocaml/eventSource.ml: why is data 'string' not 'any'?

zeroexcuses · June 2, 2023, 1:42pm

Source:

ocsigen/js_of_ocaml/blob/master/lib/js_of_ocaml/eventSource.ml#L34


      
          
          
type state =
            | CONNECTING
            | OPEN
            | CLOSED
          
          
class type ['a] messageEvent =
            object
              inherit ['a] Dom.event
          
          
    method data : js_string t readonly_prop
          
          
    method origin : js_string t readonly_prop
          
          
    method lastEventId : js_string t readonly_prop
              (* method source : unit *)
            end
          
          
class type eventSource =
            object ('self)
              method url : string t readonly_prop

class type ['a] messageEvent =
  object
    inherit ['a] Dom.event

    method data : js_string t readonly_prop

    method origin : js_string t readonly_prop

    method lastEventId : js_string t readonly_prop
    (* method source : unit *)
  end

Yet, if we read the MDN docs:

this field can be ANY Js object.

Why is js_of_ocaml making this change ?

Context: playing with postMessage/onMessage, where the payload is arbitrary JS value, not necessarily a string.