Adjust instanceof checks (#1500)

packages/util/src/is/error.ts

@@ -16,5 +16,8 @@
  * ```
  */
 export function isError (value: unknown): value is Error {
-  return value instanceof Error;
+  return (
+    ((value && (value as Record<string, unknown>).constructor) === Error) ||
+    value instanceof Error
+  );
 }

packages/util/src/is/instanceOf.ts

@@ -17,5 +17,8 @@
  */
 // eslint-disable-next-line @typescript-eslint/ban-types
 export function isInstanceOf (value: unknown, clazz: Function): boolean {
-  return value instanceof clazz;
+  return (
+    ((value && (value as Record<string, unknown>).constructor) === clazz) ||
+    value instanceof Uint8Array
+  );
 }

packages/util/src/is/u8a.spec.ts

@@ -1,6 +1,7 @@
 // Copyright 2017-2022 @polkadot/util authors & contributors
 // SPDX-License-Identifier: Apache-2.0
 
+import { performance } from '../test/performance';
 import { isU8a } from '.';
 
 describe('isU8a', (): void => {
@@ -10,6 +11,12 @@ describe('isU8a', (): void => {
     ).toEqual(false);
   });
 
+  it('returns false on null values', (): void => {
+    expect(
+      isU8a(null)
+    ).toEqual(false);
+  });
+
   it('returns false on Array values', (): void => {
     expect(
       isU8a([1, 2, 3])
@@ -28,4 +35,6 @@ describe('isU8a', (): void => {
       isU8a(new Uint8Array())
     ).toEqual(true);
   });
+
+  performance('isU8a', 2_000_000, [[new Uint8Array()]], isU8a);
 });

packages/util/src/is/u8a.ts

@@ -16,5 +16,10 @@
  * ```
  */
 export function isU8a (value?: unknown): value is Uint8Array {
-  return value instanceof Uint8Array;
+  // here we defer the instanceof check which is actually slightly
+  // slower than just checking the constrctor (direct instances)
+  return (
+    ((value && (value as Record<string, unknown>).constructor) === Uint8Array) ||
+    value instanceof Uint8Array
+  );
 }