feat: support returning a Promise from the filter utility function (#…

…2291)
dotansimha · Jan 5, 2023 · fe4a2ac · fe4a2ac
1 parent 97f962d
commit fe4a2ac
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Showing 3 changed files with 27 additions and 4 deletions.
diff --git a/.changeset/eighty-pigs-know.md b/.changeset/eighty-pigs-know.md
@@ -0,0 +1,9 @@
+---
+'@graphql-yoga/subscription': minor
+---
+
+Support returning a `Promise` from the `filter` utility function.
+
+```ts
+const applyFilter = filter((value) => Promise.resolve(value > 3))
+```
diff --git a/packages/subscription/src/operator/filter.spec.ts b/packages/subscription/src/operator/filter.spec.ts
@@ -12,7 +12,6 @@ async function collectAsyncIterableValues<TType>(
 
 describe('filter', () => {
   it('filters source stream', async () => {
-    // eslint-disable-next-line @typescript-eslint/require-await
     async function* source() {
       yield 1
       yield 2
@@ -26,4 +25,19 @@ describe('filter', () => {
 
     expect(result).toEqual([1, 2, 1])
   })
+
+  it('async filter is supported', async () => {
+    async function* source() {
+      yield 1
+      yield 2
+      yield 3
+      yield 1
+    }
+
+    const filterFn = (value: number) => Promise.resolve(value < 3)
+    const stream = filter(filterFn)(source())
+    const result = await collectAsyncIterableValues(stream)
+
+    expect(result).toEqual([1, 2, 1])
+  })
 })
diff --git a/packages/subscription/src/operator/filter.ts b/packages/subscription/src/operator/filter.ts
@@ -7,9 +7,9 @@ export function filter<T, U extends T>(
   filter: (input: T) => input is U,
 ): (source: AsyncIterable<T>) => Repeater<U, void, unknown>
 export function filter<T>(
-  filter: (input: T) => boolean,
+  filter: (input: T) => Promise<boolean> | boolean,
 ): (source: AsyncIterable<T>) => Repeater<T, void, unknown>
-export function filter(filter: (value: unknown) => boolean) {
+export function filter(filter: (value: unknown) => Promise<boolean> | boolean) {
   return (source: AsyncIterable<unknown>) =>
     new Repeater(async (push, stop) => {
       const iterable = source[Symbol.asyncIterator]()
@@ -19,7 +19,7 @@ export function filter(filter: (value: unknown) => boolean) {
 
       let latest: IteratorResult<unknown>
       while ((latest = await iterable.next()).done === false) {
-        if (filter(latest.value)) {
+        if (await filter(latest.value)) {
           await push(latest.value)
         }
       }