Invoking an object as a function in Kotlin JS

Some JavaScript libraries provide function objects with additional members. Expressing these as Kotlin objects in external class declarations is somewhat difficult. They can be given an operator fun invoke and called like a function using method call syntax, but the compiler will produce a call to an invoke method that doesn't exist. That could be re-@JsNamed to call and appear to work in some cases, but it's not really the right thing to do since call has the special behavior of setting this.

The expected approach seems to be to drop to weak typing by reinterpreting the object as a function. The class can be given an inline extension operator invoke along these lines:

inline operator fun Express.invoke(): ExpressApp {

    return this.unsafeCast<() -> ExpressApp>()()

}

Alternatively the receiver can be treated as the dynamic type:

inline operator fun Express.invoke(): ExpressApp {

    return this.asDynamic()() as ExpressApp

}