diff --git a/src/vs/base/common/types.ts b/src/vs/base/common/types.ts
index 980c686c9ad..42eea76fe40 100644
--- a/src/vs/base/common/types.ts
+++ b/src/vs/base/common/types.ts
@@ -5,45 +5,25 @@
 
 import { URI, UriComponents } from 'vs/base/common/uri';
 
-const _typeof = {
-	number: 'number',
-	string: 'string',
-	undefined: 'undefined',
-	object: 'object',
-	function: 'function'
-};
-
 /**
  * @returns whether the provided parameter is a JavaScript Array or not.
  */
 export function isArray(array: any): array is any[] {
-	if (Array.isArray) {
-		return Array.isArray(array);
-	}
-
-	if (array && typeof (array.length) === _typeof.number && array.constructor === Array) {
-		return true;
-	}
-
-	return false;
+	return Array.isArray(array);
 }
 
 /**
  * @returns whether the provided parameter is a JavaScript String or not.
  */
 export function isString(str: any): str is string {
-	if (typeof (str) === _typeof.string || str instanceof String) {
-		return true;
-	}
-
-	return false;
+	return (typeof str === 'string');
 }
 
 /**
  * @returns whether the provided parameter is a JavaScript Array and each element in the array is a string.
  */
 export function isStringArray(value: any): value is string[] {
-	return isArray(value) && (<any[]>value).every(elem => isString(elem));
+	return Array.isArray(value) && (<any[]>value).every(elem => isString(elem));
 }
 
 /**
@@ -55,7 +35,7 @@ export function isObject(obj: any): obj is Object {
 	// The method can't do a type cast since there are type (like strings) which
 	// are subclasses of any put not positvely matched by the function. Hence type
 	// narrowing results in wrong results.
-	return typeof obj === _typeof.object
+	return typeof obj === 'object'
 		&& obj !== null
 		&& !Array.isArray(obj)
 		&& !(obj instanceof RegExp)
@@ -67,32 +47,28 @@ export function isObject(obj: any): obj is Object {
  * @returns whether the provided parameter is a JavaScript Number or not.
  */
 export function isNumber(obj: any): obj is number {
-	if ((typeof (obj) === _typeof.number || obj instanceof Number) && !isNaN(obj)) {
-		return true;
-	}
-
-	return false;
+	return (typeof obj === 'number' && !isNaN(obj));
 }
 
 /**
  * @returns whether the provided parameter is a JavaScript Boolean or not.
  */
 export function isBoolean(obj: any): obj is boolean {
-	return obj === true || obj === false;
+	return (obj === true || obj === false);
 }
 
 /**
  * @returns whether the provided parameter is undefined.
  */
 export function isUndefined(obj: any): obj is undefined {
-	return typeof (obj) === _typeof.undefined;
+	return (typeof obj === 'undefined');
 }
 
 /**
  * @returns whether the provided parameter is undefined or null.
  */
 export function isUndefinedOrNull(obj: any): obj is undefined | null {
-	return isUndefined(obj) || obj === null;
+	return (isUndefined(obj) || obj === null);
 }
 
 
@@ -158,7 +134,7 @@ export function isEmptyObject(obj: any): obj is any {
  * @returns whether the provided parameter is a JavaScript Function or not.
  */
 export function isFunction(obj: any): obj is Function {
-	return typeof obj === _typeof.function;
+	return (typeof obj === 'function');
 }
 
 /**
diff --git a/src/vs/workbench/api/common/extHostTypes.ts b/src/vs/workbench/api/common/extHostTypes.ts
index 1612a967bfe..5b14380f8aa 100644
--- a/src/vs/workbench/api/common/extHostTypes.ts
+++ b/src/vs/workbench/api/common/extHostTypes.ts
@@ -16,7 +16,7 @@ import { FileSystemProviderErrorCode, markAsFileSystemProviderError } from 'vs/p
 import { RemoteAuthorityResolverErrorCode } from 'vs/platform/remote/common/remoteAuthorityResolver';
 import type * as vscode from 'vscode';
 import { Cache } from './cache';
-import { assertIsDefined } from 'vs/base/common/types';
+import { assertIsDefined, isStringArray } from 'vs/base/common/types';
 import { Schemas } from 'vs/base/common/network';
 
 function es5ClassCompat(target: Function): any {
@@ -2427,18 +2427,7 @@ export class SemanticTokensLegend {
 }
 
 function isStrArrayOrUndefined(arg: any): arg is string[] | undefined {
-	if (typeof arg === 'undefined') {
-		return true;
-	}
-	if (Array.isArray(arg)) {
-		for (const element of arg) {
-			if (typeof element !== 'string') {
-				return false;
-			}
-		}
-		return true;
-	}
-	return false;
+	return ((typeof arg === 'undefined') || isStringArray(arg));
 }
 
 export class SemanticTokensBuilder {