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kotlinlang

Just confirming here, based on what I've seen in several threads, there is currently no type-safe way to support Union Types in KotlinJS? I'm fine with just returning `dynamic`, but just wanted to confirm.

You can sometimes emulate union types in parameters of external functions using overloading:
```
// .ts
function foo(x: string|number): void
// .kt
external fun foo(x: Double)
external fun foo(x: String)
```

Yeah unfortunately the union type is the return type of a callback in a `var`

Generic constraints can help with intersection types but not union types

Rust solved this problem nicely with the `Into` and `From` traits :disappointed: