From 9f83f87480caa99bbb807200b3f55eb1f27a8789 Mon Sep 17 00:00:00 2001
From: futpib <futpib@gmail.com>
Date: Sat, 6 Aug 2022 02:42:27 +0400
Subject: [PATCH] Add an `off` method to promise returned from `once`

---
 index.d.ts      | 11 +++++++++--
 index.js        | 11 ++++++++---
 index.test-d.ts |  3 +++
 test/index.js   | 24 ++++++++++++++++++++++++
 4 files changed, 44 insertions(+), 5 deletions(-)

diff --git a/index.d.ts b/index.d.ts
index de19515..9429799 100644
--- a/index.d.ts
+++ b/index.d.ts
@@ -132,6 +132,13 @@ interface Options<EventData> {
 	debug?: DebugOptions<EventData>;
 }
 
+/**
+A promise returned from `emittery.once` with an extra `off` method to cancel your subscription.
+*/
+interface EmitteryOncePromise<T> extends Promise<T> {
+	off(): void;
+}
+
 /**
 Emittery is a strictly typed, fully async EventEmitter implementation. Event listeners can be registered with `on` or `once`, and events can be emitted with `emit`.
 
@@ -436,7 +443,7 @@ declare class Emittery<
 	Subscribe to one or more events only once. It will be unsubscribed after the first
 	event.
 
-	@returns The event data when `eventName` is emitted.
+	@returns The promise of event data when `eventName` is emitted. This promise is extended with an `off` method.
 
 	@example
 	```
@@ -457,7 +464,7 @@ declare class Emittery<
 	emitter.emit('🐶', '🍖'); // Nothing happens
 	```
 	*/
-	once<Name extends keyof AllEventData>(eventName: Name | Name[]): Promise<AllEventData[Name]>;
+	once<Name extends keyof AllEventData>(eventName: Name | Name[]): EmitteryOncePromise<AllEventData[Name]>;
 
 	/**
 	Trigger an event asynchronously, optionally with some data. Listeners are called in the order they were added, but executed concurrently.
diff --git a/index.js b/index.js
index 09c2fcc..e8eaabb 100644
--- a/index.js
+++ b/index.js
@@ -283,12 +283,17 @@ class Emittery {
 	}
 
 	once(eventNames) {
-		return new Promise(resolve => {
-			const off = this.on(eventNames, data => {
-				off();
+		let off_;
+
+		const promise = new Promise(resolve => {
+			off_ = this.on(eventNames, data => {
+				off_();
 				resolve(data);
 			});
 		});
+
+		promise.off = off_;
+		return promise;
 	}
 
 	events(eventNames) {
diff --git a/index.test-d.ts b/index.test-d.ts
index 8fb41a2..2bd77fa 100644
--- a/index.test-d.ts
+++ b/index.test-d.ts
@@ -54,6 +54,9 @@ type AnyListener = (eventData?: unknown) => void | Promise<void>;
 			expectType<PropertyKey | undefined>(eventName);
 			expectType<AnyListener>(listener);
 		});
+		const oncePromise = ee.once('anotherEvent');
+		oncePromise.off();
+		await oncePromise;
 	};
 }
 
diff --git a/test/index.js b/test/index.js
index 566c47d..7de7788 100644
--- a/test/index.js
+++ b/test/index.js
@@ -374,6 +374,30 @@ test('once() - eventName must be a string, symbol, or number', async t => {
 	await t.throwsAsync(emitter.once(true), TypeError);
 });
 
+test('once() - returns a promise with an unsubscribe method', async t => {
+	const fixture = '🌈';
+	const emitter = new Emittery();
+	const oncePromise = emitter.once('🦄');
+
+	const testFailurePromise = Promise.race([
+		(async () => {
+			await oncePromise;
+			t.fail();
+		})(),
+		new Promise(resolve => {
+			setTimeout(() => {
+				resolve(false);
+			}, 100);
+		})
+	]);
+
+	oncePromise.off();
+	emitter.emit('🦄', fixture);
+
+	await testFailurePromise;
+	t.pass();
+});
+
 test.cb('emit() - one event', t => {
 	t.plan(1);