Can the copy function of data classes be used in K...

# javascript

[Alexander Weickmann]

Can the copy function of data classes be used in KotlinJS? I get "Uncaught TypeError: copy is not a function"

[turansky]

You need custom named wrapper for generic case

[Alexander Weickmann]

How would this need to look like?

[Alexander Weickmann]

Can you give an example?

[turansky]

data class D(val a: Int) {
    @JsName("copy")
    fun jsCopy(val a: Int?): D = copy(a = a)
}

[turansky]

I think you want copy with single options parameter. Right?

[turansky]

Options will be more flexible in this case

[turansky]

@Alexander Weickmann Options example - https://pl.kotl.in/3fHjFCNQ6

[turansky]

But I think in JS world must be used spread operator on plain data object instead for clear solution and #serialization on Kotlin side

[Alexander Weickmann]

@turansky it works, but we cannot add this code to the multiplatform common module data class 😞

[turansky]

Do you use IR?

[Alexander Weickmann]

we found a solution:

@Suppress("UnsafeCastFromDynamic")
fun <T> T.jsCopy(options: dynamic.() -> Unit): T {
    val o = this
    val copyObj = js("Object.assign({}, o)")

    val optionsObj = jsObject(options)
    Object.keys(optionsObj).forEach { key ->
        val descriptor = Object.getOwnPropertyDescriptor<RProps>(optionsObj, key)
        Object.defineProperty(copyObj, key, descriptor)
        undefined
    }

    return copyObj as T
}

inline fun jsObject(init: dynamic.() -> Unit): dynamic {
    val o = js("{}")
    init(o)
    return o
}

[Alexander Weickmann]

what is IR?

[turansky]

Looks like you create unsafe #serialization

[turansky]

IR - new compiler (in alpha now)

[Alexander Weickmann]

no, we are not using the alpha compiler. what do you mean by unsafe serialization? is there another approach available how we could do this? we are using react / redux and it is very important to have the ability to copy objects with a certain value being changed.

[turansky]

I use legacy compiler too.
I use DynamicObjectParser for converting Data classes to JSO, on JS side I use spread operator - standard JS functionality.

[turansky]

@Alexander Weickmann Do you need example of such solution? I have one