Fix asPromise race condition

packages/@react-facet/core/src/helpers/asPromise.spec.ts

@@ -1,10 +1,28 @@
+import { NO_VALUE } from '..'
 import { createFacet } from '../facet'
 import { asPromise } from './asPromise'
 
-it('resolves facets with their values if available', async () => {
+it('immediately resolves facets with their values if available', async () => {
  const facet = createFacet({ initialValue: 'testing' })
- const value = await asPromise(facet)
+ const value = await asPromise(facet).promise
  expect(value).toEqual('testing')
 })
 
-it.todo('waits for the facet to have a value, making sure to not hold subscriptions')
+it('waits for the facet to have a value, making sure to not hold subscriptions', async () => {
+ const cleanupSubscription = jest.fn()
+ const startSubscription = jest.fn().mockImplementation((update) => {
+ update('testing')
+ return cleanupSubscription
+ })
+
+ const facet = createFacet<string>({
+ initialValue: NO_VALUE,
+ startSubscription,
+ })
+
+ const value = await asPromise(facet).promise
+ expect(value).toEqual('testing')
+
+ expect(startSubscription).toHaveBeenCalledTimes(1)
+ expect(cleanupSubscription).toHaveBeenCalledTimes(1)
+})

packages/@react-facet/core/src/helpers/asPromise.ts

@@ -1,21 +1,37 @@
 import { Facet, NO_VALUE } from '../types'
 
 /**
- * Takes a Facet as returns a Promise that will resolve with its first value
+ * Takes a Facet and returns a Promise that will resolve with its first value
  *
  * @param facet
  * @returns Promise<T>
  */
-export const asPromise = <T>(facet: Facet<T>) =>
- new Promise<T>((resolve) => {
- const value = facet.get()
- if (value !== NO_VALUE) {
- resolve(value)
- return
+export const asPromise = <T>(facet: Facet<T>) => {
+ let resolve: (value: T | PromiseLike<T>) => void = noop
+
+ const promise = new Promise<T>((_resolve) => {
+ resolve = _resolve
+ })
+
+ const value = facet.get()
+ if (value !== NO_VALUE) {
+ resolve(value)
+
+ return {
+ promise,
+ cancel: noop,
  }
+ }
 
- const cleanup = facet.observe((value: T) => {
- resolve(value)
+ const cleanup = facet.observe(resolve)
+
+ return {
+ promise: promise.then((value) => {
  cleanup()
- })
- })
+ return value
+ }),
+ cancel: cleanup,
+ }
+}
+
+const noop = () => {}