Repository: sindresorhus/is (ts)

Issue:
Add `.asyncGenerator` detection
https://jakearchibald.com/2017/async-iterators-and-generators/

Pull request description:
Add `.asyncGenerator` and `.asyncGeneratorFunction` detection
Fixes #99

Patch:
diff --git a/readme.md b/readme.md
index 12a4809..d274bb3 100644
--- a/readme.md
+++ b/readme.md
@@ -132,6 +132,38 @@ is.asyncFunction(() => {});
 // => false
 ```
 
+##### .asyncGenerator(value)
+
+```js
+is.asyncGenerator(
+	(async function * () {
+		yield 4;
+	})()
+);
+// => true
+
+is.asyncGenerator(
+	(function * () {
+		yield 4;
+	})()
+);
+// => false
+```
+
+##### .asyncGeneratorFunction(value)
+
+```js
+is.asyncGeneratorFunction(async function * () {
+	yield 4;
+});
+// => true
+
+is.asyncGeneratorFunction(function * () {
+	yield 4;
+});
+// => false
+```
+
 ##### .boundFunction(value)
 
 Returns `true` for any `bound` function.
diff --git a/source/index.ts b/source/index.ts
index 8eb85d2..4d42bfe 100644
--- a/source/index.ts
+++ b/source/index.ts
@@ -14,7 +14,9 @@ export const enum TypeName {
 	symbol = 'symbol',
 	Function = 'Function',
 	Generator = 'Generator',
+	AsyncGenerator = 'AsyncGenerator',
 	GeneratorFunction = 'GeneratorFunction',
+	AsyncGeneratorFunction = 'AsyncGeneratorFunction',
 	AsyncFunction = 'AsyncFunction',
 	Observable = 'Observable',
 	Array = 'Array',
@@ -141,6 +143,8 @@ is.asyncIterable = <T = unknown>(value: unknown): value is AsyncIterableIterator
 
 is.generator = (value: unknown): value is Generator => is.iterable(value) && is.function_(value.next) && is.function_(value.throw);
 
+is.asyncGenerator = (value: unknown): value is AsyncGenerator => is.asyncIterable(value) && is.function_(value.next) && is.function_(value.throw);
+
 is.nativePromise = <T = unknown>(value: unknown): value is Promise<T> =>
 	isObjectOfType<Promise<T>>(TypeName.Promise)(value);
 
@@ -153,6 +157,8 @@ is.promise = <T = unknown>(value: unknown): value is Promise<T> => is.nativeProm
 
 is.generatorFunction = isObjectOfType<GeneratorFunction>(TypeName.GeneratorFunction);
 
+is.asyncGeneratorFunction = (value: unknown): value is ((...args: any[]) => Promise<unknown>) => getObjectType(value) === TypeName.AsyncGeneratorFunction;
+
 is.asyncFunction = <T = unknown>(value: unknown): value is ((...args: any[]) => Promise<T>) => getObjectType(value) === TypeName.AsyncFunction;
 
 // eslint-disable-next-line no-prototype-builtins, @typescript-eslint/ban-types
@@ -454,9 +460,11 @@ interface Assert {
 	iterable: <T = unknown>(value: unknown) => asserts value is Iterable<T>;
 	asyncIterable: <T = unknown>(value: unknown) => asserts value is AsyncIterable<T>;
 	generator: (value: unknown) => asserts value is Generator;
+	asyncGenerator: (value: unknown) => asserts value is AsyncGenerator;
 	nativePromise: <T = unknown>(value: unknown) => asserts value is Promise<T>;
 	promise: <T = unknown>(value: unknown) => asserts value is Promise<T>;
 	generatorFunction: (value: unknown) => asserts value is GeneratorFunction;
+	asyncGeneratorFunction: (value: unknown) => asserts value is AsyncGeneratorFunction;
 	// eslint-disable-next-line @typescript-eslint/ban-types
 	asyncFunction: (value: unknown) => asserts value is Function;
 	// eslint-disable-next-line @typescript-eslint/ban-types
@@ -542,9 +550,11 @@ export const assert: Assert = {
 	iterable: <T = unknown>(value: unknown): asserts value is Iterable<T> => assertType(is.iterable(value), AssertionTypeDescription.iterable, value),
 	asyncIterable: <T = unknown>(value: unknown): asserts value is AsyncIterable<T> => assertType(is.asyncIterable(value), AssertionTypeDescription.asyncIterable, value),
 	generator: (value: unknown): asserts value is Generator => assertType(is.generator(value), TypeName.Generator, value),
+	asyncGenerator: (value: unknown): asserts value is AsyncGenerator => assertType(is.asyncGenerator(value), TypeName.AsyncGenerator, value),
 	nativePromise: <T = unknown>(value: unknown): asserts value is Promise<T> => assertType(is.nativePromise(value), AssertionTypeDescription.nativePromise, value),
 	promise: <T = unknown>(value: unknown): asserts value is Promise<T> => assertType(is.promise(value), TypeName.Promise, value),
 	generatorFunction: (value: unknown): asserts value is GeneratorFunction => assertType(is.generatorFunction(value), TypeName.GeneratorFunction, value),
+	asyncGeneratorFunction: (value: unknown): asserts value is AsyncGeneratorFunction => assertType(is.asyncGeneratorFunction(value), TypeName.AsyncGeneratorFunction, value),
 	// eslint-disable-next-line @typescript-eslint/ban-types
 	asyncFunction: (value: unknown): asserts value is Function => assertType(is.asyncFunction(value), TypeName.AsyncFunction, value),
 	// eslint-disable-next-line @typescript-eslint/ban-types


Test patch:
diff --git a/test/test.ts b/test/test.ts
index eb681bc..f48b7c3 100644
--- a/test/test.ts
+++ b/test/test.ts
@@ -156,7 +156,8 @@ const types = new Map<string, Test>([
 			function () {},
 			() => {},
 			async function () {},
-			function * (): unknown {}
+			function * (): unknown {},
+			async function * (): unknown {}
 		],
 		typename: TypeName.Function
 	}],
@@ -232,6 +233,16 @@ const types = new Map<string, Test>([
 		],
 		typename: TypeName.Generator
 	}],
+	['asyncGenerator', {
+		is: is.asyncGenerator,
+		assert: assert.asyncGenerator,
+		fixtures: [
+			(async function * () {
+				yield 4;
+			})()
+		],
+		typename: TypeName.AsyncGenerator
+	}],
 	['generatorFunction', {
 		is: is.generatorFunction,
 		assert: assert.generatorFunction,
@@ -243,6 +254,17 @@ const types = new Map<string, Test>([
 		typename: TypeName.Function,
 		typeDescription: TypeName.GeneratorFunction
 	}],
+	['asyncGeneratorFunction', {
+		is: is.asyncGeneratorFunction,
+		assert: assert.asyncGeneratorFunction,
+		fixtures: [
+			async function * () {
+				yield 4;
+			}
+		],
+		typename: TypeName.Function,
+		typeDescription: TypeName.AsyncGeneratorFunction
+	}],
 	['asyncFunction', {
 		is: is.asyncFunction,
 		assert: assert.asyncFunction,
@@ -609,7 +631,7 @@ test('is.array', t => {
 });
 
 test('is.function', t => {
-	testType(t, 'function', ['generatorFunction', 'asyncFunction', 'boundFunction']);
+	testType(t, 'function', ['generatorFunction', 'asyncGeneratorFunction', 'asyncFunction', 'boundFunction']);
 });
 
 test('is.boundFunction', t => {
@@ -678,10 +700,33 @@ test('is.generator', t => {
 	testType(t, 'generator');
 });
 
+test('is.asyncGenerator', t => {
+	testType(t, 'asyncGenerator');
+
+	const fixture = (async function * () {
+		yield 4;
+	})();
+	if (is.asyncGenerator(fixture)) {
+		t.true(is.function_(fixture.next));
+	}
+});
+
 test('is.generatorFunction', t => {
 	testType(t, 'generatorFunction', ['function']);
 });
 
+test('is.asyncGeneratorFunction', t => {
+	testType(t, 'asyncGeneratorFunction', ['function']);
+
+	const fixture = async function * () {
+		yield 4;
+	};
+
+	if (is.asyncGeneratorFunction(fixture)) {
+		t.true(is.function_(fixture().next));
+	}
+});
+
 test('is.map', t => {
 	testType(t, 'map', ['emptyMap']);
 });