i noticed that data class copy() methods don't hav...

# javascript

[prashan]

i noticed that data class copy() methods don't have default parameters (pretty much making them useless), even though javascript seems to support it: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Functions/Default_parameters is there a ticket for this i can follow?

[jw]

Many ES6/ES2015 features are not used

[jw]

You can finally target ES6 and get some, but I suspect post-K2 we'll get more

[prashan]

ah yeah i see that https://youtrack.jetbrains.com/issue/KT-8373/JS-support-ES6-as-compilation-target is "fixed" in 2.0.0

[prashan]

closing the loop here after trying to target ES6, seems like default parameters aren't used yet

[prashan]

actually upon digging some more: Kotlin JS generates a function like this:

// Kotlin
data class TestDataClass(val test: String)

// Generated JS
protoOf(TestDataClass).copy = function (test, $super) {
  test = test === VOID ? this.test : test;
  return this.i(test);
};

and VOID here is defined as js("void 0") which evaluates to undefined (https://github.com/JetBrains/kotlin/blob/master/libraries/stdlib/js/runtime/void.kt)

so we can at least somewhat get the desired copy behavior by passing in undefined to the fields you want to keep the same.