How to return JSObject from JSFunction?

Question

I'd like to return a reference to a Javascript object from an FFI function definition in order to be able to manipulate the object later on:

import           Data.Aeson
import           Foreign.JavaScript (JSObject, NewJSObject, unsafeCreateJSObject)
import           Foreign.RemotePtr (RemotePtr)
import           Graphics.UI.Threepenny.Core hiding (text)

mkJSObject :: JSFunction NewJSObject -> UI JSObject
mkJSObject f = askWindow >>= liftIO . flip unsafeCreateJSObject f

polyLine :: [[Double]] -> Value -> UI JSObject
polyLine points = mkJSObject . f points
  where
    f :: [[Double]] -> Value -> JSFunction NewJSObject
    f = ffi "L.polyline(%1, %2).addTo(map)"

But the underlying Javascript Window doesn't seem to be publicly accessible. Is there another way for creating references to Javascript objects?

That looks fine to me. It appears to me that you have answered your own question? — Heinrich Apfelmus, Sep 27 '16 at 12:14
Yes, but maybe the answer is helpful for others, too. Thanks for threepenny-gui btw, well designed and extremely useful! — kaoskorobase, Sep 27 '16 at 12:48
Of course. :-) But could you cut the answer and paste it below? That would make it easier for others to understand later. And thank you, I'm glad you like it. :-) — Heinrich Apfelmus, Sep 27 '16 at 18:02
There doesn't seem to be an option for answering my own question, I can just add comments. Could you maybe add the answer? Thanks! — kaoskorobase, Sep 29 '16 at 19:05
Sorry, forget it, I hadn't seen the big blue button at the bottom ;) — kaoskorobase, Sep 29 '16 at 19:08

score 1 · Answer 1 · answered Sep 29 '16 at 19:07

It's actually much simpler: Just return a JSObject from JSFunction and it will be marshalled correctly:

polyLine :: [[Double]] -> Value -> UI JSObject
polyLine points = callFunction . f points
  where
    f :: [[Double]] -> Value -> JSFunction JSObject
    f = ffi "L.polyline(%1, %2).addTo(map)"

How to return JSObject from JSFunction?

1 Answers1