feat: new export getParent

README.md

@@ -109,6 +109,7 @@ $: yarn add @maverick-js/observables
 - [`onDispose`](#ondispose)
 - [`isObservable`](#isobservable)
 - [`isSubject`](#issubject)
+- [`getParent`](#getparent)
 - [`getScheduler`](#getscheduler)
 
 ## `$root`
@@ -392,6 +393,18 @@ isSubject($computed(() => 10));
 isSubject($readonly($observable(10)));
 ```
 
+### `getParent`
+
+Returns the parent/owner of the given function (if defined). You can use this function to
+recursively walk up the computation tree (useful for implementing a context API).
+
+```js
+$root(() => {
+  const $a = $observable(0);
+  getParent($a); // returns `$root`
+});
+```
+
 ### `getScheduler`
 
 Returns the global scheduler which can be used to queue additional tasks or synchronously flush

src/observables.ts

@@ -22,6 +22,7 @@ export type MaybeObservable<T> = MaybeFunction | Observable<T>;
 
 const NOOP = () => {};
 
+const PARENT = Symbol();
 const OBSERVABLE = Symbol();
 const COMPUTED = Symbol();
 const DIRTY = Symbol();
@@ -279,6 +280,7 @@ export function $dispose(fn: () => void) {
   unrefSet(fn, DISPOSAL);
   unrefSet(fn, OBSERVERS);
 
+  fn[PARENT] = undefined;
   fn[DIRTY] = false;
   fn[DISPOSED] = true;
 }
@@ -379,6 +381,22 @@ export function isSubject<T>(fn: MaybeObservable<T>): fn is ObservableSubject<T>
   return isObservable(fn) && !!(fn as ObservableSubject<T>).set;
 }
 
+/**
+ * Returns the parent/owner of the given function (if defined). You can use this to walk up
+ * the computation tree.
+ *
+ * @example
+ * ```js
+ * $root(() => {
+ *   const $a = $observable(0);
+ *   getParent($a); // returns `$root`
+ * });
+ * ```
+ */
+export function getParent(fn: Observable<unknown>): Observable<unknown> | undefined {
+  return fn[PARENT];
+}
+
 /**
  * Returns the global scheduler.
  */
@@ -416,7 +434,10 @@ function compute<T>(parent: () => void, child: () => T): T {
 }
 
 function adoptChild(node: Node) {
-  if (_parent) addChild(_parent, node);
+  if (_parent) {
+    node[PARENT] = _parent;
+    addChild(_parent, node);
+  }
 }
 
 function addChild(node: Node, child: Node) {

tests/getParent.test.ts

@@ -0,0 +1,40 @@
+import { $effect, $observable, $peek, $root, getParent } from '../src';
+
+it('should be orphan', () => {
+  const $a = $observable(0);
+  expect(getParent($a)).toBeUndefined();
+});
+
+it('should return parent', () => {
+  $root(() => {
+    const $a = $observable(0);
+    expect(getParent($a)).toBeInstanceOf(Function);
+  });
+});
+
+it('should return parent from inside peek', () => {
+  $root(() => {
+    $peek(() => {
+      const $a = $observable(0);
+      expect(getParent($a)).toBeInstanceOf(Function);
+    });
+  });
+});
+
+it('should return grandparent', () => {
+  $root(() => {
+    $effect(() => {
+      const $a = $observable(0);
+      expect(getParent($a)).toBeInstanceOf(Function);
+      expect(getParent(getParent($a)!)).toBeInstanceOf(Function);
+    });
+  });
+});
+
+it('should remove parent on dispose', () => {
+  $root((dispose) => {
+    const $a = $observable(0);
+    dispose();
+    expect(getParent($a)).toBeUndefined();
+  });
+});