deferred helper, might be useful

src/helpers/deferred.test.ts

@@ -0,0 +1,14 @@
+import test from "ava"
+import { deferred } from "./deferred.js"
+
+test("resolve", async (t) => {
+  const d = deferred<string>()
+  setTimeout(() => d.resolve("hi"))
+  t.is(await d, "hi")
+})
+
+test("reject", async (t) => {
+  const d = deferred()
+  setTimeout(() => d.reject(new Error("oops")))
+  await t.throwsAsync(() => d, { instanceOf: Error, message: "oops" })
+})

src/helpers/deferred.ts

@@ -0,0 +1,20 @@
+export type Deferred<T> = PromiseLike<T> & {
+  resolve: (value: T | PromiseLike<T>) => void
+  reject: (reason?: unknown) => void
+}
+
+export function deferred<T = void>(): Deferred<T> {
+  let resolve: (value: T | PromiseLike<T>) => void
+  let reject: (reason?: unknown) => void
+
+  const promise = new Promise<T>((_resolve, _reject) => {
+    resolve = _resolve
+    reject = _reject
+  })
+
+  return {
+    then: promise.then.bind(promise),
+    resolve: (value) => resolve(value),
+    reject: (reason) => reject(reason),
+  }
+}