tests for is.class and readme info

index.js

@@ -62,6 +62,7 @@ is.symbol = x => typeof x === 'symbol';
 
 is.array = Array.isArray;
 is.function = x => typeof x === 'function';
+is.class = x => typeof x === 'function' && x.toString().startsWith('class ');
 is.buffer = Buffer.isBuffer;
 
 is.object = x => {
@@ -130,7 +131,7 @@ is.plainObject = x => {
 	// eslint-disable-next-line no-return-assign
 	return getObjectType(x) === 'Object' &&
 		(prototype = Object.getPrototypeOf(x), prototype === null ||
-		prototype === Object.getPrototypeOf({}));
+			prototype === Object.getPrototypeOf({}));
 };
 
 is.iterable = x => !is.null(x) && !is.undefined(x) && typeof x[Symbol.iterator] === 'function';

readme.md

@@ -64,6 +64,10 @@ All the below methods accept a value and returns a boolean for whether the value
 #### Built-in types
 
 ##### .array(value)
+##### .class(value)
+
+Returns `true` for any function that initialized as an ES6 class.
+
 ##### .function(value)
 ##### .buffer(value)
 ##### .object(value)

test.js

@@ -6,6 +6,8 @@ const isNode8orHigher = Number(process.versions.node.split('.')[0]) >= 8;
 
 const PromiseSubclassFixture = class extends Promise {};
 const ErrorSubclassFixture = class extends Error {};
+const FooClassFixture = class Foo {};
+const BarClassFixture = class Bar extends FooClassFixture {};
 
 const types = new Map([
 	['undefined', undefined],
@@ -28,6 +30,9 @@ const types = new Map([
 		[1, 2],
 		new Array(2)
 	]],
+	['class', [
+		new BarClassFixture()
+	]],
 	['function', [
 		function foo() {}, // eslint-disable-line func-names
 		function () {},
@@ -130,6 +135,10 @@ test('is.array', t => {
 	testType(t, 'array');
 });
 
+test('is.class', t => {
+	t.true(types.get('class')[0] instanceof FooClassFixture);
+});
+
 test('is.function', t => {
 	testType(t, 'function');
 });