Upgrade Jest

There was an unfortunate quirk of upgrading Jest. They changed their
node globals to include an `ArrayBuffer` override, synchronizing the
value with `Buffer.from([]).buffer.constructor`. I didn't dive too deep,
but what became clear was `new Uint8Array(0).buffer` and
`Buffer.from([]).buffer` reference different `ArrayBuffer` constructors.
This failed the tests because I was comparing the constructor from two
separate realms.

See: jestjs/jest#7626

This affects production code, not just tests. Because the global
constructor was different between environments, it forced me to check by
string tag instead of instance. That's probably a good change anyway.

I manually checked the string tag in Node, IE11, Firefox, and Chrome.

CHANGELOG.md

@@ -4,7 +4,10 @@
 
 ## Unreleased
 ### Removed
-- Dropped support for unmaintained node versions (node < 8).
+- Dropped support for unmaintained node versions (node < 10).
+
+### Fixed
+- Improve cross-realm detection of `ArrayBuffer` instances.
 
 ## 0.3.1
 ### Changed

package.json

@@ -56,7 +56,7 @@
     "eslint-config-prettier": "^6.10.0",
     "eslint-plugin-prettier": "^3.1.3",
     "husky": "^4.2.5",
-    "jest": "^25.1.0",
+    "jest": "^26.0.1",
     "lint-staged": "^10.2.6",
     "prettier": "^2.0.5"
   },

src/__tests__/index.test.js

@@ -1,5 +1,6 @@
 import { small, large } from '../strings';
 import json from '../index';
+import { NativeArrayBuffer } from '../test-utils';
 
 const originalSecretKey = json.SECRET_KEY;
 
@@ -27,7 +28,7 @@ describe('bin-json', () => {
   it('encodes to an ArrayBuffer', () => {
     const buffer = json.encode('data');
 
-    expect(buffer).toEqual(expect.any(ArrayBuffer));
+    expect(buffer).toBeInstanceOf(NativeArrayBuffer);
   });
 
   it('works with boolean values', () => {

src/__tests__/packager.test.js

@@ -2,6 +2,7 @@ import { readFileSync } from 'fs';
 
 import { pack, unpack } from '../packager';
 import { small, large } from '../strings';
+import { NativeArrayBuffer } from '../test-utils';
 
 const createBuffer = (arrayBuffer) => Buffer.from(arrayBuffer);
 
@@ -10,7 +11,7 @@ describe('Package', () => {
     const data = Buffer.from('something');
     const buffer = pack([data]);
 
-    expect(buffer).toEqual(expect.any(ArrayBuffer));
+    expect(buffer).toBeInstanceOf(NativeArrayBuffer);
 
     const expected = Buffer.from(`${data.byteLength}\0something`);
     expect(Buffer.from(buffer)).toEqual(expected);
@@ -53,7 +54,7 @@ describe('Package', () => {
     const buffers = unpack(buffer);
 
     expect(buffers).toEqual(expect.any(Array));
-    buffers.map((buffer) => expect(buffer).toEqual(expect.any(ArrayBuffer)));
+    buffers.map((buffer) => expect(buffer).toBeInstanceOf(NativeArrayBuffer));
     expect(buffers.map(createBuffer)).toEqual([buff1, buff2]);
   });
 

src/index.js

@@ -1,6 +1,9 @@
 import { pack, unpack } from './packager';
 import { large } from './strings';
 
+// Safer than comparing by reference - cross-realm constructors can bite you.
+const ARRAY_BUFFER_TAG = '[object ArrayBuffer]';
+
 let BufferType = null;
 
 /**
@@ -36,7 +39,7 @@ const isBuffer = (data) => {
   }
 
   // Typed arrays.
-  if (data.buffer instanceof ArrayBuffer) {
+  if (Object.prototype.toString.call(data.buffer) === ARRAY_BUFFER_TAG) {
     return true;
   }
 

src/test-utils.js

@@ -0,0 +1,3 @@
+// This is not the same as `global.ArrayBuffer`. See:
+// https://github.com/facebook/jest/issues/7780
+export const NativeArrayBuffer = new Uint8Array().buffer.constructor;