feat(asyncDropOnce): add asyncDropOnce function

Author: djcsdy

index.test.ts

@@ -1,6 +1,7 @@
 import type {ExecutionContext} from "ava";
 import test from "ava";
 import {
+    asyncDropOnce,
     asyncEmptyOnce,
     asyncInitialOnce,
     asyncIterator,
@@ -171,3 +172,13 @@ test("asyncTakeOnce", async t => {
     );
     t.deepEqual(await asyncToArrayOnce(asyncTakeOnce(asyncIterator([1, 2, 3, 4, 5]), 0)), []);
 });
+
+test("asyncDropOnce", async t => {
+    t.deepEqual(await asyncToArrayOnce(asyncDropOnce(asyncIterator([]), 3)), []);
+    t.deepEqual(await asyncToArrayOnce(asyncDropOnce(asyncIterator([1, 2]), 3)), []);
+    t.deepEqual(await asyncToArrayOnce(asyncDropOnce(asyncIterator([1, 2, 3, 4, 5]), 3)), [4, 5]);
+    t.deepEqual(
+        await asyncToArrayOnce(asyncDropOnce(asyncIterator([1, 2, 3, 4, 5]), 0)),
+        [1, 2, 3, 4, 5]
+    );
+});

index.ts

@@ -275,3 +275,30 @@ export function asyncTakeOnceFn<T>(
 ): (iterator: AsyncIteratorLike<T>) => AsyncIterator<T> {
     return iterator => asyncTakeOnce(iterator, count);
 }
+
+export function asyncDropOnce<T>(
+    iterator: AsyncIteratorLike<T>,
+    count: number | Promise<number>
+): AsyncIterator<T> {
+    const it = asyncIterator(iterator);
+    let i = 0;
+    const before = async (): Promise<IteratorResult<T>> => {
+        let element = await it.next();
+        const c = await count;
+        while (i++ < c && element.done !== true) {
+            element = await it.next();
+        }
+
+        next = during;
+        return element;
+    };
+    const during = async (): Promise<IteratorResult<T>> => it.next();
+    let next = before;
+    return {next: async () => next()};
+}
+
+export function asyncDropOnceFn<T>(
+    count: number | Promise<number>
+): (iterator: AsyncIteratorLike<T>) => AsyncIterator<T> {
+    return iterator => asyncDropOnce(iterator, count);
+}