From c25b606c3bda79f82fbe506e1c3b1116c3e0eaef Mon Sep 17 00:00:00 2001
From: Sindre Sorhus <sindresorhus@gmail.com>
Date: Thu, 7 Nov 2019 16:28:20 +0700
Subject: [PATCH] Improve the type assertion for `is.asyncFunction`

---
 package.json    | 2 +-
 source/index.ts | 3 +--
 test/test.ts    | 6 ++++++
 3 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/package.json b/package.json
index 1ffa0e6..1bb1f91 100644
--- a/package.json
+++ b/package.json
@@ -59,7 +59,7 @@
 		"rxjs": "^6.4.0",
 		"tempy": "^0.3.0",
 		"ts-node": "^8.3.0",
-		"typescript": "^3.4.1",
+		"typescript": "^3.7.2",
 		"xo": "^0.25.3",
 		"zen-observable": "^0.8.8"
 	},
diff --git a/source/index.ts b/source/index.ts
index 2cfe2c3..90ca4c6 100644
--- a/source/index.ts
+++ b/source/index.ts
@@ -152,8 +152,7 @@ is.promise = (value: unknown): value is Promise<unknown> => is.nativePromise(val
 
 is.generatorFunction = isObjectOfType<GeneratorFunction>(TypeName.GeneratorFunction);
 
-// eslint-disable-next-line @typescript-eslint/ban-types
-is.asyncFunction = isObjectOfType<Function>(TypeName.AsyncFunction);
+is.asyncFunction = (value: unknown): value is ((...args: any[]) => Promise<unknown>) => getObjectType(value) === TypeName.AsyncFunction;
 
 // eslint-disable-next-line no-prototype-builtins, @typescript-eslint/ban-types
 is.boundFunction = (value: unknown): value is Function => is.function_(value) && !value.hasOwnProperty('prototype');
diff --git a/test/test.ts b/test/test.ts
index cbf59b0..0d9c13a 100644
--- a/test/test.ts
+++ b/test/test.ts
@@ -560,6 +560,12 @@ test('is.promise', t => {
 
 test('is.asyncFunction', t => {
 	testType(t, 'asyncFunction', ['function']);
+
+	const fixture = async () => {};
+	if (is.asyncFunction(fixture)) {
+		// eslint-disable-next-line promise/prefer-await-to-then
+		t.true(is.function_(fixture().then));
+	}
 });
 
 test('is.generator', t => {