Hey guys, how can one implement/call/create/whatev...

# javascript

[Jan Stoltman]

Hey guys, how can one implement/call/create/whatever a kotlin interface from JS?

[Jan Stoltman]

I have an interface in K/JS and I would like to pass its implementation to a method, which also is defined at the kotlin side, all from JS

[Svyatoslav Kuzmich [JB]]

K/JS interfaces do not correspond to anything idiomatic in JS. If absolutely necessary, you can see what K/JS compiler generates for interface implementation and try to mimic that. For example:

// Kotlin
interface I
class C : I
// Generated JS
  function I() {
  }
  I.$metadata$ = {
    kind: Kind_INTERFACE,
    simpleName: 'I',
    interfaces: []
  };
  function C() {
  }
  C.$metadata$ = {
    kind: Kind_CLASS,
    simpleName: 'C',
    interfaces: [I]
  };

If you own K/JS code with given interface you can:
a. make abstract class in K/JS and extend it like a regular JS class
b. make interface external and create JS objects with matching structure

[Jan Stoltman]

What's the difference between external and normal interfaces for JS?

[Svyatoslav Kuzmich [JB]]

It has some restrictions: https://kotlinlang.org/docs/reference/js-interop.html#external-interfaces

[Svyatoslav Kuzmich [JB]]

And guarantees for as-is member names in JS

[Jan Stoltman]

That's nice, thank you!

[U75957]

@Svyatoslav Kuzmich [JB] @Jan Stoltman

And guarantees for as-is member names in JS

Not guarantees)

https://kotlinlang.slack.com/archives/C0B8L3U69/p1559335458013500
https://kotlinlang.slack.com/archives/C0B8L3U69/p1559335973015500

[Svyatoslav Kuzmich [JB]]

@U75957 We do hear that people need more control over whether property:
- is on prototype or on object itself
- is enumerable
- has value or accessor descriptor

But name guarantees for @JsName or external properties are still there. What looks like a mangled property is likely a property's backing field which is not supposed to be accessed directly.