feat(push): add push function

Author: djcsdy

index.test.ts

@@ -1,8 +1,13 @@
 import test from "ava";
-import {asyncIterable, tail, toArray} from "./index";
+import {asyncIterable, push, tail, toArray} from "./index";
 
 test("tail", async t => {
     t.deepEqual(await toArray(tail(asyncIterable([1, 2, 3, 4]))), [2, 3, 4]);
     t.deepEqual(await toArray(tail(asyncIterable([1]))), []);
     t.deepEqual(await toArray(tail(asyncIterable([]))), []);
 });
+
+test("push", async t => {
+    t.deepEqual(await toArray(push(asyncIterable([1, 2, 3]), 4)), [1, 2, 3, 4]);
+    t.deepEqual(await toArray(push(asyncIterable([]), 4)), [4]);
+});

index.ts

@@ -52,3 +52,19 @@ export async function* tail<T>(iterable: AsyncIterableLike<T>): AsyncIterable<T>
 }
 
 export const asyncTail = tail;
+
+export async function* push<T>(iterable: AsyncIterableLike<T>, value: T): AsyncIterable<T> {
+    for await (const element of await iterable) {
+        yield element;
+    }
+
+    yield value;
+}
+
+export const asyncPush = push;
+
+export function pushFn<T>(value: T): (iterable: AsyncIterableLike<T>) => AsyncIterable<T> {
+    return iterable => push(iterable, value);
+}
+
+export const asyncPushFn = pushFn;