diff --git a/.travis.yml b/.travis.yml
index 7d69d74..e0cc348 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -2,4 +2,3 @@ language: node_js
 node_js:
   - '8'
   - '6'
-  - '4'
diff --git a/package.json b/package.json
index 0ae7c8b..5cc8aba 100644
--- a/package.json
+++ b/package.json
@@ -11,7 +11,7 @@
 	},
 	"main": "dist/index.js",
 	"engines": {
-		"node": ">=4"
+		"node": ">=6"
 	},
 	"scripts": {
 		"lint": "tslint --format stylish --project .",
@@ -44,16 +44,16 @@
 		"compare"
 	],
 	"devDependencies": {
-		"@types/jsdom": "^2.0.31",
-		"@types/node": "^8.0.47",
+		"@types/jsdom": "^11.0.4",
+		"@types/node": "^9.6.0",
 		"@types/tempy": "^0.1.0",
 		"ava": "*",
 		"del-cli": "^1.1.0",
-		"jsdom": "^9.12.0",
+		"jsdom": "^11.6.2",
 		"tempy": "^0.2.1",
-		"tslint": "^5.8.0",
-		"tslint-xo": "^0.3.0",
-		"typescript": "^2.7.0"
+		"tslint": "^5.9.1",
+		"tslint-xo": "^0.7.0",
+		"typescript": "^2.8.1"
 	},
 	"types": "dist/index.d.ts"
 }
diff --git a/source/index.ts b/source/index.ts
index 8d82479..540dd06 100644
--- a/source/index.ts
+++ b/source/index.ts
@@ -8,6 +8,8 @@ export const enum TypeName {
 	number = 'number',
 	symbol = 'symbol',
 	Function = 'Function',
+	GeneratorFunction = 'GeneratorFunction',
+	AsyncFunction = 'AsyncFunction',
 	Array = 'Array',
 	Buffer = 'Buffer',
 	Object = 'Object',
@@ -46,9 +48,7 @@ const getObjectType = (value: any): TypeName | null => {
 	return null;
 };
 
-const isObjectOfType = (typeName: TypeName) => (value: any) => {
-	return getObjectType(value) === typeName;
-};
+const isObjectOfType = (type: TypeName) => (value: any) => getObjectType(value) === type;
 
 function is(value: any): TypeName { // tslint:disable-line:only-arrow-functions
 	if (value === null) {
@@ -110,12 +110,10 @@ namespace is { // tslint:disable-line:no-namespace
 	export const number = isOfType('number');
 	export const function_ = isOfType('function');
 	export const null_ = (value: any) => value === null;
-
 	export const class_ = (value: any) => function_(value) && value.toString().startsWith('class ');
 	export const boolean = (value: any) => value === true || value === false;
-	// tslint:enable:variable-name
-
 	export const symbol = isOfType('symbol');
+	// tslint:enable:variable-name
 
 	export const array = Array.isArray;
 	export const buffer = Buffer.isBuffer;
@@ -135,11 +133,9 @@ namespace is { // tslint:disable-line:no-namespace
 
 	export const promise = (value: any) => nativePromise(value) || hasPromiseAPI(value);
 
-	// TODO: Change to use `isObjectOfType` once Node.js 6 or higher is targeted
-	const isFunctionOfType = (type: string) => (value: any) => function_(value) && function_(value.constructor) && value.constructor.name === type;
-
-	export const generatorFunction = isFunctionOfType('GeneratorFunction');
-	export const asyncFunction = isFunctionOfType('AsyncFunction');
+	const isFunctionOfType = (type: TypeName) => (value: any) => isObjectOfType(type)(value);
+	export const generatorFunction = isFunctionOfType(TypeName.GeneratorFunction);
+	export const asyncFunction = isFunctionOfType(TypeName.AsyncFunction);
 	export const boundFunction = (value: any) => function_(value) && !value.hasOwnProperty('prototype');
 
 	export const regExp = isObjectOfType(TypeName.RegExp);
@@ -164,9 +160,7 @@ namespace is { // tslint:disable-line:no-namespace
 	export const sharedArrayBuffer = isObjectOfType(TypeName.SharedArrayBuffer);
 	export const dataView = isObjectOfType(TypeName.DataView);
 
-	// TODO: Remove `object` checks when targeting ES2015 or higher
-	// See `Notes`: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/getPrototypeOf
-	export const directInstanceOf = (instance: any, klass: any) => object(instance) && object(klass) && Object.getPrototypeOf(instance) === klass.prototype;
+	export const directInstanceOf = (instance: any, klass: any) => Object.getPrototypeOf(instance) === klass.prototype;
 
 	export const truthy = (value: any) => Boolean(value);
 	export const falsy = (value: any) => !value;
@@ -225,8 +219,7 @@ namespace is { // tslint:disable-line:no-namespace
 		}
 
 		if (array(range) && range.length === 2) {
-			// TODO: Use spread operator here when targeting Node.js 6 or higher
-			return value >= Math.min.apply(null, range) && value <= Math.max.apply(null, range);
+			return value >= Math.min(...range) && value <= Math.max(...range);
 		}
 
 		throw new TypeError(`Invalid range: ${util.inspect(range)}`);
@@ -260,13 +253,8 @@ namespace is { // tslint:disable-line:no-namespace
 	export const empty = (value: any) => falsy(value) || isEmptyStringOrArray(value) || isEmptyObject(value) || isEmptyMapOrSet(value);
 	export const emptyOrWhitespace = (value: any) => empty(value) || isWhiteSpaceString(value);
 
-	type ArrayMethod = (fn: (value: any, index: number, arr: any[]) => boolean, thisArg?: any) => boolean;
-	const predicateOnArray = (method: ArrayMethod, predicate: any, args: IArguments) => {
-		// `args` is the calling function's "arguments object".
-		// We have to do it this way to keep node v4 support.
-		// So here we convert it to an array and slice off the first item.
-		const values = Array.prototype.slice.call(args, 1);
-
+	type ArrayMethod = (fn: (value: any, index: number, array: any[]) => boolean, thisArg?: any) => boolean;
+	const predicateOnArray = (method: ArrayMethod, predicate: any, values: any[]) => {
 		if (function_(predicate) === false) {
 			throw new TypeError(`Invalid predicate: ${util.inspect(predicate)}`);
 		}
@@ -278,19 +266,10 @@ namespace is { // tslint:disable-line:no-namespace
 		return method.call(values, predicate);
 	};
 
-	// We can't use rest parameters in node v4 due to the lack of the spread operator.
-	// Therefore We have to use anonymous functions for the any() and all() methods
-	// tslint:disable:only-arrow-functions no-function-expression
-	export function any(...predicate: any[]): any; // tslint:disable-line:variable-name
-	export function any(predicate: any) {
-		return predicateOnArray(Array.prototype.some, predicate, arguments);
-	}
-
-	export function all(...predicate: any[]): any;
-	export function all(predicate: any) {
-		return predicateOnArray(Array.prototype.every, predicate, arguments);
-	}
-	// tslint:enable:only-arrow-functions no-function-expression
+	// tslint:disable variable-name
+	export const any = (predicate: any, ...values: any[]) => predicateOnArray(Array.prototype.some, predicate, values);
+	export const all = (predicate: any, ...values: any[]) => predicateOnArray(Array.prototype.every, predicate, values);
+	// tslint:enable variable-name
 }
 
 // Some few keywords are reserved, but we'll populate them for Node.js users
diff --git a/source/tests/test.ts b/source/tests/test.ts
index cb1008c..64edaed 100644
--- a/source/tests/test.ts
+++ b/source/tests/test.ts
@@ -4,17 +4,16 @@ import * as Stream from 'stream';
 import * as util from 'util';
 import * as tempy from 'tempy';
 import test, {TestContext, Context} from 'ava';
-import {jsdom} from 'jsdom';
+import {JSDOM} from 'jsdom';
 import m from '..';
 
 const isNode8orHigher = Number(process.versions.node.split('.')[0]) >= 8;
 
-// Currently not working. See https://github.com/Microsoft/TypeScript/issues/15202
-// `class PromiseSubclassFixture<T> extends Promise<T> {}`
-
+class PromiseSubclassFixture<T> extends Promise<T> {}
 class ErrorSubclassFixture extends Error {}
 
-const document = jsdom();
+const {window} = new JSDOM();
+const {document} = window;
 const createDomElement = (el: string) => document.createElement(el);
 
 interface Test {
@@ -122,7 +121,7 @@ const types = new Map<string, Test>([
 		is: m.nativePromise,
 		fixtures: [
 			Promise.resolve(),
-			// PromiseSubclassFixture.resolve()
+			PromiseSubclassFixture.resolve()
 		]
 	}],
 	['promise', {