Observable. Observable.flatMap and Observable.switchMap (#2776)

Author: turansky

kotlin-web/src/commonMain/kotlin/web/observable/Observable.kt

@@ -33,7 +33,7 @@ external class Observable<T : JsAny?>(
 
     fun first(options: SubscribeOptions? = definedExternally): Promise<T>
 
-    // fun flatMap(Mapper mapper) : Observable
+    fun <R : JsAny?> flatMap(transform: (T) -> ReadonlyArray<R>): Observable<R>
 
     fun forEach(
         action: (item: T) -> Unit,
@@ -71,7 +71,7 @@ external class Observable<T : JsAny?>(
         options: SubscribeOptions? = definedExternally,
     )
 
-    // fun switchMap(Mapper mapper) : Observable
+    fun <R : JsAny?> switchMap(transform: (T) -> ReadonlyArray<R>): Observable<R>
 
     fun take(n: Int): Observable<T>