From fe344fd7eb6b0cdbc9557e8382881cc5856f36ec Mon Sep 17 00:00:00 2001
From: Brandon Smith <brandon93s@gmail.com>
Date: Sat, 9 Dec 2017 00:01:39 -0500
Subject: [PATCH] Add is.directInstanceOf()

---
 readme.md            | 14 ++++++++++++++
 source/index.ts      |  2 ++
 source/tests/test.ts | 11 +++++++++++
 3 files changed, 27 insertions(+)

diff --git a/readme.md b/readme.md
index a0d135d..95dc7c2 100644
--- a/readme.md
+++ b/readme.md
@@ -136,6 +136,20 @@ is.boundFunction(function () {});
 
 #### Miscellaneous
 
+##### .directInstanceOf(value, klass)
+
+Returns `true` if value is a direct instance of a class of type `klass`.
+
+```js
+class ErrorSubclass extends Error {};
+
+is.directInstanceOf(new Error(), Error);
+//=> true
+
+is.directInstanceOf(new ErrorSubclass(), Error);
+//=> false
+```
+
 ##### .truthy(value)
 
 Returns `true` for all values that evaluate to true in a boolean context:
diff --git a/source/index.ts b/source/index.ts
index 196a49c..97bd0cb 100644
--- a/source/index.ts
+++ b/source/index.ts
@@ -162,6 +162,8 @@ namespace is { // tslint:disable-line:no-namespace
 	export const arrayBuffer = isObjectOfType(TypeName.ArrayBuffer);
 	export const sharedArrayBuffer = isObjectOfType(TypeName.SharedArrayBuffer);
 
+	export const directInstanceOf = (instance: any, klass: any) => object(instance) && object(klass) && Object.getPrototypeOf(instance) === klass.prototype;
+
 	export const truthy = (value: any) => Boolean(value);
 	export const falsy = (value: any) => !value;
 
diff --git a/source/tests/test.ts b/source/tests/test.ts
index 340defd..130594b 100644
--- a/source/tests/test.ts
+++ b/source/tests/test.ts
@@ -507,6 +507,17 @@ test('is.dataView', t => {
 	testType(t, 'arrayBuffer');
 });
 
+test('is.directInstanceOf', t => {
+	const error = new Error();
+	const errorSubclass = new ErrorSubclassFixture();
+
+	t.true(m.directInstanceOf(error, Error));
+	t.true(m.directInstanceOf(errorSubclass, ErrorSubclassFixture));
+
+	t.false(m.directInstanceOf(error, ErrorSubclassFixture));
+	t.false(m.directInstanceOf(errorSubclass, Error));
+});
+
 test('is.truthy', t => {
 	t.true(m.truthy('unicorn'));
 	t.true(m.truthy('🦄'));