feat(asyncPrependOnce): add asyncPrependOnce function

Author: djcsdy

index.test.ts

@@ -35,6 +35,7 @@ import {
     asyncOnlyOnce,
     asyncOrOnce,
     asyncPrefixMatchOnce,
+    asyncPrependOnce,
     asyncPushOnce,
     asyncRemoveFirstOnce,
     asyncRemoveOnce,
@@ -533,3 +534,22 @@ test("asyncConcatOnce", async t => {
         []
     );
 });
+
+test("asyncPrependOnce", async t => {
+    t.deepEqual(
+        await asyncToArrayOnce(
+            asyncPrependOnce(asyncIterator([1, 2, 3]))(asyncIterator([4, 5, 6]))
+        ),
+        [1, 2, 3, 4, 5, 6]
+    );
+    t.deepEqual(
+        await asyncToArrayOnce(
+            asyncPrependOnce(asyncIterator<number>([]))(asyncIterator([4, 5, 6]))
+        ),
+        [4, 5, 6]
+    );
+    t.deepEqual(
+        await asyncToArrayOnce(asyncPrependOnce(asyncIterator([1, 2, 3]))(asyncIterator([]))),
+        [1, 2, 3]
+    );
+});

index.ts

@@ -1029,3 +1029,9 @@ export function asyncConcatOnce<T>(
     let next = first;
     return {next: async () => next()};
 }
+
+export function asyncPrependOnce<T>(
+    a: AsyncIteratorLike<T>
+): (b: AsyncIteratorLike<T>) => AsyncIterator<T> {
+    return b => asyncConcatOnce([a, b]);
+}