Anyone has an idea what could cause this error: ```kotlin-react-tutorial.js?92c2:40758 Uncaught Type...

# javascript

[dave08]

Anyone has an idea what could cause this error:

kotlin-react-tutorial.js?92c2:40758 Uncaught TypeError: Cannot read property 'toString' of undefined
    at _no_name_provided__132.invoke_223 (kotlin-react-tutorial.js?92c2:40758)
    at _no_name_provided__83.eval [as _$render] (kotlin-react-tutorial.js?92c2:40780)
    at _no_name_provided__83.invoke_132 (kotlin-react-tutorial.js?92c2:24110)
    at eval (kotlin-react-tutorial.js?92c2:24149)
    at buildElements (kotlin-react-tutorial.js?92c2:23965)
    at _no_name_provided__84.invoke_134 (kotlin-react-tutorial.js?92c2:24124)
    at VideoList (kotlin-react-tutorial.js?92c2:24136)
    at renderWithHooks (react-dom.development.js?b313:14985)
    at updateFunctionComponent (react-dom.development.js?b313:17356)
    at beginWork (react-dom.development.js?b313:19063)

In here:

_no_name_provided__132.prototype.invoke_223 = function ($this$rFunction, props) {
    var tmp0_iterator = props.videos.iterator_68();
    while (tmp0_iterator.hasNext_49()) {
      var video = tmp0_iterator.next_56();
      var tmp0_p_0 = null;
      var tmp1_tag_0_1 = _no_name_provided_$factory_98(tmp0_p_0);
      var tmp0_apply_0_3 = new RDOMBuilder(tmp1_tag_0_1);
>>>      tmp0_apply_0_3._set_key_(video._id.toString()); <<<<<<
      var tmp0__anonymous__1_5 = tmp0_apply_0_3._attrs_0;
      _set_onClickFunction_(tmp0__anonymous__1_5, _no_name_provided_$factory_99(props, video));
      if (video.equals(props.selectedVideo)) {
        tmp0_apply_0_3.unaryPlus_8('\u25B6 ');
      }tmp0_apply_0_3.unaryPlus_8('' + video._speaker + ': ' + video._title);
      $this$rFunction.child_4(tmp0_apply_0_3.create_11());
      Unit_getInstance();
    }
  };

I'm using the IR compiler in dev mode

[Marc Knaup]

How do that function and class Video look like in Kotlin?

[dave08]

The id is an Int

[Marc Knaup]

I mean please share some code. Otherwise it’s difficult to help 🙂

[andylamax]

I remember having the same error. Mine was caused by unsafeCast

So in your case, if you unsafely cast the id to an int that might by the problem\

[dave08]

data class Video(val id: Int, val title: String, val speaker: String, val videoUrl: String)

[dave08]

val videoList = rFunction<VideoListProps>("VideoList") { props ->
   for (video in props.videos) {
      p {
         key = video.id.toString()

[dave08]

it fails at the key = assignment

[Marc Knaup]

How do you set the props?

[dave08]

videoList {
   attrs.videos = unwatchedVideos
   attrs.selectedVideo = currentVideo
   attrs.onSelectVideo = { video ->
      setCurrentVideo(video)
   }
}

[andylamax]

how do you get unwatchedVideos

[dave08]

val app = rFunction<RProps>("App") {
   val (currentVideo, setCurrentVideo) = useState<Video?>(null)
   val (unwatchedVideos, setUnwatchedVideos) = useState<List<Video>>(listOf())
   val (watchedVideos, setWatchedVideos) = useState<List<Video>>(listOf())

   useEffect(listOf()) {
      val mainScope = MainScope()
      mainScope.launch {
         val videos = fetchVideos()
         setUnwatchedVideos(videos)
      }
   }

[dave08]

suspend fun fetchVideo(id: Int): Video =
   window.fetch("<https://my-json-server.typicode.com/kotlin-hands-on/kotlinconf-json/videos/$id>")
      .await()
      .json()
      .await()
      .unsafeCast<Video>()


suspend fun fetchVideos(): List<Video> = coroutineScope {
   (1..25).map { id ->
      async {
         fetchVideo(id)
      }
   }.awaitAll()
}

[dave08]

It's from the kotlin js tutorial...

[Marc Knaup]

There’s your unsafeCast. hmm]

[dave08]

I just upgraded deps and switched to IR and the fun started 😄

[dave08]

Before it seemed to work...

[Marc Knaup]

The tutorial doesn’t work with IR then. It relied on some compiler internals.\

[Marc Knaup]

The property used to be named id in JS but now it’s _id in IR.

[Marc Knaup]

You should use kotlinx-serialization to parse JSON from a server instead of unsafeCast which is the curlpit here.

[Marc Knaup]

Alternatively you can convert your data class Video to external interface Video. That should work as well.

[dave08]

The property used to be named id in JS but now it’s _id in IR.

why?

[dave08]

So I'd suppose that _id turns out to be null and doesn't have a toString()...

[dave08]

The Video object is internal in the kotlin code... so external interface Video would require me to write it in js?

[Marc Knaup]

why?

It’s an implementation detail how Kotlin properties are implemented in JS. So naming has changed from Legacy compiler to IR.

[Marc Knaup]

The Video object is internal in the kotlin code... so external interface Video would require me to write it in js? (edited)

No, you don’t need to implement it.

[Robert Jaros]

You can use @JsExport https://kotlinlang.org/docs/reference/js-to-kotlin-interop.html#jsexport-annotation

[Marc Knaup]

For

external interface Foo { val bar: Int }

the following is sufficient in JS:

val foo = { bar: 1 }

A simple object.

And that’s returned as JSON by your API call.

[Marc Knaup]

You can use @JsExport

There’s no need here. There’s nothing to export.

[Robert Jaros]

True

[Marc Knaup]

@Sebastian Aigner the tutorial needs an update here, esp. for the IR compiler. That unsafeCast() for parsed JSON to data class is really dangerous 😉

https://play.kotlinlang.org/hands-on/Building%20Web%20Applications%20with%20React%20and%20Kotlin%20JS/08_Using_an_External_REST_API

[Sebastian Aigner]

Absolutely right. That was a compromise that was made to work around some other stuff at the time. That’ll be updated.

[dave08]

Thanks for the explanation guys 👍🏼...

[dave08]

At the same time, you'll need to update the react-player definitions @Sebastian Aigner... I'm having problems with that too...

[Sebastian Aigner]

Sorry to hear that Dave. I’ll check it and address that in an update as well.

[dave08]

So far, I have:

@file:JsModule("react-player")
@file:JsNonModule

import react.*

external object ReactPlayer {
	val default: RClass<ReactPlayerProps>
}

external interface ReactPlayerProps : RProps {
	var url: String?
		get() = definedExternally
		set(value) = definedExternally
}

and I'm getting:

Uncaught TypeError: Cannot read property 'default' of undefined
    at VideoPlayer.render_0 (kotlin-react-tutorial.js?92c2:40913)
    at _no_name_provided__82.invoke_132 (kotlin-react-tutorial.js?92c2:24052)
    at eval (kotlin-react-tutorial.js?92c2:24142)
    at buildElements (kotlin-react-tutorial.js?92c2:23965)
    at VideoPlayer.RComponent.render_1 (kotlin-react-tutorial.js?92c2:24073)
    at VideoPlayer.RComponent.render (kotlin-react-tutorial.js?92c2:24076)
    at finishClassComponent (react-dom.development.js?b313:17485)
    at updateClassComponent (react-dom.development.js?b313:17435)
    at beginWork (react-dom.development.js?b313:19073)
    at HTMLUnknownElement.callCallback (react-dom.development.js?b313:3945)

[dave08]

And before that, I had https://youtrack.jetbrains.com/issue/KT-43195

[dave08]

Since @JsName("default") was being used...

[dave08]

It was supposed to be this 🤔:

import react.*

@JsModule("react-player")
@JsNonModule
external object ReactPlayer {
	val default: RClass<ReactPlayerProps>
}

external interface ReactPlayerProps : RProps {
	var url: String?
		get() = definedExternally
		set(value) = definedExternally
}