Fix finally to return Observable

README.md

@@ -421,7 +421,11 @@ We propose the following operators in addition to the `Observable` interface:
     until the input observable emits its first value
 - `finally()`
   - Like `Promise.finally()`, it takes a callback which gets fired after the
-    observable completes in any way (`complete()`/`error()`)
+    observable completes in any way (`complete()`/`error()`).
+  - Returns an `Observable` that mirrors the source observable exactly. The callback
+    passed to `finally` is fired when a subscription to the resulting observable is terminated
+    for _any reason_. Either immediately after the source completes or errors, or when the consumer
+    unsubscribes by aborting the subscription.
 
 Versions of the above are often present in userland implementations of
 observables as they are useful for observable-specific reasons, but in addition

spec.bs

@@ -335,8 +335,6 @@ interface Observable {
   constructor(SubscribeCallback callback);
   undefined subscribe(optional ObserverUnion observer = {}, optional SubscribeOptions options = {});
 
-  undefined finally(VoidFunction callback);
-
   // Constructs a native Observable from value if it's any of the following:
   //   - Observable
   //   - AsyncIterable
@@ -354,6 +352,7 @@ interface Observable {
   Observable take(unsigned long long amount);
   Observable drop(unsigned long long amount);
   Observable flatMap(Mapper mapper);
+  Observable finally(VoidFunction callback);
 
   // Promise-returning operators.
   Promise<sequence<any>> toArray(optional SubscribeOptions options = {});
@@ -688,6 +687,12 @@ For now, see [https://github.com/wicg/observable#operators](https://github.com/w
     1. <span class=XXX>TODO: Spec this and use |mapper|.</span>
 </div>
 
+<div algorithm>
+  The <dfn for=Observable method><code>finally(|callback|)</code></dfn> method steps are:
+
+    1. <span class=XXX>TODO: Spec this and use |callback|.</span>
+</div>
+
 
 <h4 id=promise-returning-operators>{{Promise}}-returning operators</h4>