kotlin-stdlib/kotlin.js/then

then

inline fun <T, S> Promise<Promise<T>>.then(noinline onFulfilled: (T) -> S?): Promise<S>(source)
inline fun <T, S> Promise<Promise<T>>.then(noinline onFulfilled: (T) -> S?, noinline onRejected: (Throwable) -> S?): Promise<S>(source)

Since Kotlin

1.1