feat(asyncPrefixMatchOnce): add asyncPrefixMatchOnce function

Author: djcsdy

index.test.ts

@@ -12,6 +12,7 @@ import {
     asyncNotEmptyOnce,
     asyncNotEqualOnce,
     asyncOnlyOnce,
+    asyncPrefixMatchOnce,
     asyncPushOnce,
     asyncSliceOnce,
     asyncTailOnce,
@@ -326,3 +327,11 @@ test("asyncNotEqualOnce", async t => {
         )
     );
 });
+
+test("asyncPrefixMatchOnce", async t => {
+    t.true(await asyncPrefixMatchOnce(asyncIterator([]), asyncIterator([])));
+    t.true(await asyncPrefixMatchOnce(asyncIterator([1, 2, 3]), asyncIterator([])));
+    t.true(await asyncPrefixMatchOnce(asyncIterator([1, 2, 3, 4]), asyncIterator([1, 2])));
+    t.false(await asyncPrefixMatchOnce(asyncIterator([1, 3, 4]), asyncIterator([1, 2])));
+    t.false(await asyncPrefixMatchOnce(asyncIterator([]), asyncIterator([1])));
+});

index.ts

@@ -461,3 +461,21 @@ export function asyncNotEqualOnceFn<T>(
 ): (a: AsyncIteratorLike<T>) => Promise<boolean> {
     return async a => !(await asyncEqualOnce(a, b, elementsEqual));
 }
+
+export async function asyncPrefixMatchOnce<T>(
+    a: AsyncIteratorLike<T>,
+    b: AsyncIteratorLike<T>,
+    elementsEqual: (a: T, b: T) => boolean | Promise<boolean> = defaultEqual
+): Promise<boolean> {
+    const ait = asyncIterator(a);
+    const bit = asyncIterator(b);
+    let [aElement, bElement] = await Promise.all([ait.next(), bit.next()] as const);
+    while (
+        aElement.done !== true &&
+        bElement.done !== true &&
+        (await elementsEqual(aElement.value, bElement.value))
+    ) {
+        [aElement, bElement] = await Promise.all([ait.next(), bit.next()] as const);
+    }
+    return bElement.done === true;
+}