Port Subscription Not working on initial load on 0.17

[knowthen]

Background: I was trying to pull in a JWT from localstorage using ports and I'm unable to do it on initial page load.

Summary: Elm Msg via port subscription, not generated on initial load, however it does work when triggered via button press

To provide a simplified example, I took the source from the interop section of the gitbook and slightly modified it as follows:

init : (Model, Cmd Msg)
init =
  -- (Model "" [], Cmd.none)
  (Model "" [], check "" )

I put a console.log into the javascript side and I can see that the handler on the js side is getting called

app.ports.check.subscribe(function(word) {
      console.log('js subscribe fired..');
      // put some dummy data in
      // var suggestions = spellCheck(word);
      var suggestions = ["Junk", "Jump"];
      app.ports.suggestions.send(suggestions);
    });

however the response app.ports.suggestions.send(suggestions); doesn't seem to create message on the elm side.

Oddly if I click the "check" button, a message (from the subscription) is created.

Here's a repo with the code demonstrating the apparent bug: https://github.com/knowthen/portbug

[schnittchen]

I have the same problem here, and it sometimes works and sometimes doesn't.

I debugged around a bit and found this: Stepping into the port send has subs an empty (Elm) list here https://github.com/elm-lang/core/blob/master/src/Native/Platform.js#L547

Maybe @knowthen can confirm this observation.

[schnittchen]

I have the same problem here, and it sometimes works and sometimes doesn't.

I debugged around a bit and found this: Stepping into the port send has subs an empty (Elm) list here https://github.com/elm-lang/core/blob/master/src/Native/Platform.js#L547

Maybe @knowthen can confirm this observation.

[CumpsD]

Same here, subs is empty, working around it with setTimeout(function(){ app.ports.jsMsgs.send(1); }, 0) for now, then they aren't empty

[CumpsD]

Same here, subs is empty, working around it with setTimeout(function(){ app.ports.jsMsgs.send(1); }, 0) for now, then they aren't empty

[PhilippMeissner]

For the moment you might be happy using programWithFlags like the TodoMVC did. That's what I did as a momentarily workaround.
Here's the documentation: http://package.elm-lang.org/packages/elm-lang/html/1.0.0/Html-App#programWithFlags

Here's it in action :
https://github.com/evancz/elm-todomvc/blob/master/Todo.elm#L86
https://github.com/evancz/elm-todomvc/blob/master/index.html#L17

Hope that helps you out for the moment. Obviously this issue still needs to be looked into.

[PhilippMeissner]

For the moment you might be happy using programWithFlags like the TodoMVC did. That's what I did as a momentarily workaround.
Here's the documentation: http://package.elm-lang.org/packages/elm-lang/html/1.0.0/Html-App#programWithFlags

Here's it in action :
https://github.com/evancz/elm-todomvc/blob/master/Todo.elm#L86
https://github.com/evancz/elm-todomvc/blob/master/index.html#L17

Hope that helps you out for the moment. Obviously this issue still needs to be looked into.

[evancz]

Going with #595 as a simpler example.

[evancz]

Going with #595 as a simpler example.