From 23a54a479cd0f5d09154c9bc33dd77555f10c328 Mon Sep 17 00:00:00 2001
From: flakey5 <73616808+flakey5@users.noreply.github.com>
Date: Fri, 27 Jan 2023 17:12:00 -0800
Subject: [PATCH] lib: AsyncLocalStorage.bind() and
 AsyncLocalStorage.snapshot()

---
 doc/api/async_context.md | 44 ++++++++++++++++++++++++++++++++++++++++
 lib/async_hooks.js       |  8 ++++++++
 2 files changed, 52 insertions(+)

diff --git a/doc/api/async_context.md b/doc/api/async_context.md
index 51092f25dcfccf..c7052215f9fb54 100644
--- a/doc/api/async_context.md
+++ b/doc/api/async_context.md
@@ -147,6 +147,50 @@ this time will print the stack trace and exit. See
 Creating an async resource within the `onPropagate` callback will result in
 a recursive call to `onPropagate`.
 
+### `asyncLocalStorage.bind(fn [, thisArg])`
+
+<!-- YAML
+added: REPLACEME
+-->
+
+* `fn` {Function} The function to bind to the current execution context.
+* `thisArg` {any}
+
+Binds the given function to the current execution context.
+
+The returned function will have an `asyncResource` property referencing
+the `AsyncResource` to which the function is bound.
+
+### `asyncLocalStorage.snapshot()`
+
+<!-- YAML
+added: REPLACEME
+-->
+
+Returns a callback that captures the current async context and invokes a
+callback passed into it within the captured async context.
+
+```js
+const asyncLocalStorage = new AsyncLocalStorage();
+const runInAsyncScope = asyncLocalStorage.run(123, () => als.snapshot());
+const result = asyncLocalStorage.run(321, () => runInAsyncScope(() => asyncLocalStorage.getStore()));
+console.log(result);  // returns 123
+```
+
+AsyncLocalStorage.snapshot() can replace the use of AsyncResource for simple
+async context tracking purposes, for example:
+
+```js
+class Foo {
+  #runInAsyncScope = AsyncLocalStorage.snapshot();
+
+  get() { return this.#runInAsyncScope(() => asyncLocalStorage.getStore()); }
+}
+
+const foo = asyncLocalStorage.run(123, () => new Foo());
+console.log(asyncLocalStorage.run(321, () => foo.get())); // returns 123
+```
+
 ### `asyncLocalStorage.disable()`
 
 <!-- YAML
diff --git a/lib/async_hooks.js b/lib/async_hooks.js
index bf76874ffe2c1b..c7908c127ae5f1 100644
--- a/lib/async_hooks.js
+++ b/lib/async_hooks.js
@@ -288,6 +288,14 @@ class AsyncLocalStorage {
     this._onPropagate = onPropagate;
   }
 
+  static bind(fn, thisArg) {
+    return new AsyncResource('bound-anonymous-fn').bind(fn, thisArg);
+  }
+
+  static snapshot() {
+    return AsyncLocalStorage.bind((cb, ...args) => cb(...args));
+  }
+
   disable() {
     if (this.enabled) {
       this.enabled = false;