From 5ad31283e436157179c859b830b250454ae0567a Mon Sep 17 00:00:00 2001
From: Dominic Farolino <domfarolino@gmail.com>
Date: Tue, 12 Sep 2023 17:40:26 +0200
Subject: [PATCH 1/4] Add `addTeardown()`. Closes #3. Closes #19.

---
 README.md | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)

diff --git a/README.md b/README.md
index f0e275e..0883e2e 100644
--- a/README.md
+++ b/README.md
@@ -307,6 +307,7 @@ interface Subscriber {
   undefined next(any result);
   undefined complete();
   undefined error(any error);
+  undefined addTeardown(VoidFunction teardown);
 
   readonly attribute AbortSignal signal;
 };
@@ -457,6 +458,33 @@ observable.subscribe({next: data => {
 }, signal: controller.signal});
 ```
 
+#### Teardown
+
+It is critical for an Observable subscriber to be able to register an arbitrary
+teardown callback to clean up any resources relevant to the subscription. The
+teardown can be registered from within the subscription callback passed into the
+`Observable` constructor. When run (upon subscribing), the subscription callback
+can register a teardown function via `subscriber.addTeardown()`.
+
+If the subscriber has already been aborted (i.e., `subscriber.signal.aborted` is
+`true`), then the given teardown callback is invoked immediately from within
+`addTeardown()`. Otherwise, it is invoked synchronously:
+
+ - From `complete()`, after the subscriber's complete handler (if any) is
+   invoked
+ - From `error()`, after the subscriber's error handler (if any) is invoked
+ - Unsubscription
+
+Note that `addTeardown(cleanup)` is just syntactic sugar over the following:
+
+```js
+if (subscriber.signal.aborted) {
+  cleanup();
+} else {
+  subscriber.signal.onabort = cleanup;
+}
+```
+
 
 ### Operators
 

From 69e0c81127ccab271c8ec2011254e756d65c0cdb Mon Sep 17 00:00:00 2001
From: Dominic Farolino <domfarolino@gmail.com>
Date: Wed, 13 Sep 2023 11:12:38 +0200
Subject: [PATCH 2/4] Remove old note

---
 README.md | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/README.md b/README.md
index 0883e2e..7eee5d6 100644
--- a/README.md
+++ b/README.md
@@ -379,9 +379,6 @@ observable.subscribe({
 });
 ```
 
-**Issue**: See https://github.com/domfarolino/observable/issues/3 about having
-the Observable constructor being able to register teardown upon unsubscription.
-
 While custom Observables can be useful on their own, the primary use case they
 unlock is with event handling. Observables returned by the new
 `EventTarget#on()` method are created natively with an internal callback that

From e8fa9fd7a5d392c3105e60b453b002066aefd624 Mon Sep 17 00:00:00 2001
From: Dominic Farolino <domfarolino@gmail.com>
Date: Wed, 13 Sep 2023 14:56:47 +0200
Subject: [PATCH 3/4] Remove the syntactic sugar analogy

The intent with that analogy was to describe how *part* of `addTeardown()`
is syntactic sugar over immediately checking `subscriber.signal.aborted`,
and *otherwise* setting the given cleanup function to the signal's abort
handler, and also invoking it during `complete()` and `error()`, but that
latter part was not clear at all and was contradictory as @annevk pointed
out. So this commit removes the example, in favor of the earlier descriptive
text.
---
 README.md | 11 -----------
 1 file changed, 11 deletions(-)

diff --git a/README.md b/README.md
index 7eee5d6..d05e161 100644
--- a/README.md
+++ b/README.md
@@ -470,17 +470,6 @@ If the subscriber has already been aborted (i.e., `subscriber.signal.aborted` is
  - From `complete()`, after the subscriber's complete handler (if any) is
    invoked
  - From `error()`, after the subscriber's error handler (if any) is invoked
- - Unsubscription
-
-Note that `addTeardown(cleanup)` is just syntactic sugar over the following:
-
-```js
-if (subscriber.signal.aborted) {
-  cleanup();
-} else {
-  subscriber.signal.onabort = cleanup;
-}
-```
 
 
 ### Operators

From 29bb984eae354daea4d60a346a5378c60dcc7433 Mon Sep 17 00:00:00 2001
From: Ben Lesh <ben@benlesh.com>
Date: Wed, 13 Sep 2023 15:51:56 +0200
Subject: [PATCH 4/4] chore: add more information about when teardown occurs.

---
 README.md | 1 +
 1 file changed, 1 insertion(+)

diff --git a/README.md b/README.md
index d05e161..d04a967 100644
--- a/README.md
+++ b/README.md
@@ -470,6 +470,7 @@ If the subscriber has already been aborted (i.e., `subscriber.signal.aborted` is
  - From `complete()`, after the subscriber's complete handler (if any) is
    invoked
  - From `error()`, after the subscriber's error handler (if any) is invoked
+ - The signal passed to the subscription is aborted by the user.
 
 
 ### Operators