New to writing Kotlin wrappers, what is the correct way to wrap an object that consumes another obje...

# javascript

[Sam Garfinkel]

New to writing Kotlin wrappers, what is the correct way to wrap an object that consumes another object (i.e. Foo({...}))?

[Svyatoslav Kuzmich [JB]]

You want describe a JS class Foo that takes an object {...} of a particular shape as a constructor parameter. Did I understand you correctly?

[Sam Garfinkel]

Yeah that's the signature of the Javascript library

[Sam Garfinkel]

I just want to write the interop code (call existing Javascript from Kotlin)

[Svyatoslav Kuzmich [JB]]

That would be

external interface FooParameter {
    // ...
}

external class Foo(p: FooParameter) {
    // ...
}

[Sam Garfinkel]

@Svyatoslav Kuzmich [JB] Thank you!

[Sam Garfinkel]

@Svyatoslav Kuzmich [JB] Is there any good way to describe an object {} with optional parameters? Suppose new Foo({}) accepts an object {A: 'foo', B: 'bar'}, where A or B may be undefined. In Kotlin we'd use default parameters on the constructor, what's the analogue for the wrapper?

[Svyatoslav Kuzmich [JB]]

You can default them to definedExternally https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.js/defined-externally.html

[Sam Garfinkel]

Thanks, I'll use that

[Svyatoslav Kuzmich [JB]]

In case of interfaces one can do

external interface I {
    var A: String? get() = definedExternally; set(value) = definedExternally
    var B: String? get() = definedExternally; set(value) = definedExternally
}

[Sam Garfinkel]

Does this mean you need to create an implementation of I each time you want to pass it to Foo?

[Svyatoslav Kuzmich [JB]]

Yes, you would need a class or object that implements I. But you can also wrap the whole thing with a regular function that uses default parameters.

[turansky]

@Sam Garfinkel Could you configure Foo after creation?

[turansky]

Via properties for example