hi, i’m an old kotlin for java user but wanted to try kotlin for js first time for a node.js project...

# javascript

[Kemal Erbakirci]

hi, i’m an old kotlin for java user but wanted to try kotlin for js first time for a node.js project.
but it doesn’t go smooth!
Unfortunately I keep getting errors.
here is my code:

@JsModule("cdktf")
@JsNonModule
open external class App()

fun main() {
    val app = App()
    println(app)
}

and here is the error message:

val app = App()
              ^
TypeError: App is not a constructor

any help will be highly appreciated

[Big Chungus]

Have a read through this to get a better understanding of kotlin externals

https://dev.to/mpetuska/js-in-kotlinjs-c4g

[Big Chungus]

Js has many module systems so wrapping approaches differ wildly across libs

[Kemal Erbakirci]

thanks @Big Chungus i’m gonna read

[Kemal Erbakirci]

this is using a ts lib from npm

[Big Chungus]

Doesn't matter since ts only lives during build time. The lib still ends up being js after publishing.

[Kemal Erbakirci]

cool, i started reading the post

[Kemal Erbakirci]

hi again, after reading your post, i had some improvement, thanks a lot. but i’m again stuck 🤦‍♂️
here’s the current version of the code:

import constructs.Construct

@JsModule("constructs")
@JsNonModule
external object constructs {
    open class Construct
}

@JsModule("cdktf")
@JsNonModule
external object cdktf {
    class App : Construct {
        fun synth(): Unit

    }
    open class TerraformStack(scope: Construct, id: String) : Construct
    class TerraformVariable(app: Construct, id: String, function: () -> Unit)
}

//////////////
class MyStack(scope: Construct, id: String) : cdktf.TerraformStack(scope, id) {
    init {
        cdktf.TerraformVariable(this, "my_var") {}
    }
}

fun main() {
    val app = <http://cdktf.App|cdktf.App>()
    MyStack(app, "ctd-infra")
    app.synth();
}

and now I get this error:

class MyStack(scope: Construct, id: String) : cdktf.TerraformStack(scope, id) {
                                              ^
ReferenceError: TerraformStack is not defined

any ideas?

[Big Chungus]

Looks like incorrect declarations. I'd need to see js/ts code you're wrapping to advise more

[Kemal Erbakirci]

hi, i saw this just now. this is the declaration of that class:
https://github.com/hashicorp/terraform-cdk/blob/main/packages/cdktf/lib/terraform-stack.ts#L61

[Big Chungus]

Ok, did some digging in my sandbox and it looks to be a bug related to extending external classes KT-56818. Everything works just fine if you don't try to extend the external class and just use it directly.

[Big Chungus]

Here's my code if you want to play with it https://github.com/mpetuska/kotlin-sandbox/tree/2a7d467fa0f42baa751e8c68433ad9c45dcb306e/modules/kjs
As a temporary workaround until it's fixed I could suggest using delegation over inheritance when bridging with external classes.

[Kemal Erbakirci]

thanks a lot Martynas for your helps! tbh, it is way more complicated than i expected…

[Big Chungus]

It is, unfortunately. Steep learning curve, but once you get a hang of it it becomes a lot easier.

[Big Chungus]

Js having shitloads of ways to export things doesn't help either

[Kemal Erbakirci]

for me this is not kotlin 😄

[Big Chungus]

Agree that it's bonkers if you have to do it yourself all the time. The saving grace is the oss community that wraps popular js libs and publishes them to maven central.