Hello. I am trying kotlin serialization to js: ```...

# javascript

[Fedor Bobin]

Hello.
I am trying kotlin serialization to js:

@Serializable
data class Test(var inner: Map<String, String>)

......

try{
            val str = """
                {
                  "inner" : {
                    "a" : "b"
                  }
                }
            """.trimIndent()

            val parsed = JSON.parse<Test>(str)
            parsed.inner.forEach {
                println(it)
            }
        }catch (e: Throwable){
            println(e.message)
        }

It prints
Cannot read property 'iterator' of undefined
because inner map is deserializable to object (not to Map).

Can you help me?

[anton.bannykh]

cc @sandwwraith

[sandwwraith]

Seems like a bug. Can you file an issue on github.com/Kotlin/kotlinx.serialization ?

[Fedor Bobin]

ok.

[Fedor Bobin]

Just found the reason: invalid import JSON was not from kotlinx.serialization but from kotlin.core. May be it should be different names or different method names?

[sandwwraith]

@anton.bannykh ?

[anton.bannykh]

@Fedor Bobin you mean kotlin.js.JSON?

[anton.bannykh]

If you do, keep in mind that kotlin.js.JSON.parse is an external declaration. Which means it just describes, what a native JS function does. That means two things. First, it doesn't make sure the resulting value type is correct. It just assumes it is. Second, in order to describe the result of JSON.parse correctly, you should use an external interface declaration. Or just Json. Or dynamic. Most importantly, don't use some Kotlin class, since the compiler will assume it has some extra feature (e.g. methods defined on the protype, some metadata, etc), and there will be nothing like that on the actual Json value, created by the javascript JSON.parse function.

[anton.bannykh]

So for example, this works:

import kotlin.js.*

external interface Test {
    val inner: Json
}

private fun Json.toMap(): Map<String, String> {
    val map: MutableMap<String, String> = linkedMapOf()
    for (key in js("Object").keys(this)) {
        map.put(key, this[key] as String)
    }
    return map
}

fun main(args: Array<String>) {
    
    val str = """
               {
                 "inner" : {
                   "a" : "b"
                 }
               }
           """.trimIndent()

    try {
           val parsed = JSON.parse<Test>(str)
           parsed.inner.toMap().forEach {
               println(it)
           }
    } catch (t: Throwable) {
        println(t.message)      
    }
}

[sandwwraith]

The question was, is it possible to suppress kotlin.js.JSON auto-import, because it’s a common issue for kotlinx-serialization-js users

[anton.bannykh]

Like this: import kotlinx.serialization.json.JSON?

[sandwwraith]

Seems like when you type JSON, idea auto-imports kotlin.js.JSON and doesn’t suggest to import kotlinx.serialization.json.JSON

[anton.bannykh]

Maybe it would make sense to move kotlinx.serialization.json.JSON to package kotlinx.serialization. This way the statement import kotlinx.serialization.* would hide the kotlin.js.JSON

[anton.bannykh]

By the way, kotlin.js.JSON is imported by default, meaning you don't have to write a single import statement in order to use it (which I personally dislike)

[sandwwraith]

that gets the problem even harder

[anton.bannykh]

We won't be able to change this until 1.3