[Bug]: jest-environment-jsdom messes with global Uint8Array

[Janpot]

Version

29.0.2

Steps to reproduce

1. clone https://github.com/Janpot/jest-esbuild-repro
2. run yarn && yarn test
3. observe failing test
4. remove testEnvironment: "jest-environment-jsdom", from 'jest.config.js'
5. observe test passing

Expected behavior

The test should pass, jsdom shouldn't touch Uint8Array if it exists in global scope

Actual behavior

the test fails, jsdom seems to have overwritten Uint8Array

Additional context

No response

Environment

System:
    OS: macOS 12.4
    CPU: (8) arm64 Apple M1
  Binaries:
    Node: 16.17.0 - ~/.nvm/versions/node/v16.17.0/bin/node
    Yarn: 1.22.19 - ~/.nvm/versions/node/v16.17.0/bin/yarn
    npm: 8.15.0 - ~/.nvm/versions/node/v16.17.0/bin/npm
  npmPackages:
    jest: ^29.0.2 => 29.0.2

[Janpot]

Ok, after reading #9983 I don't imagine this will get fixed. Closing proactively

[SimenB]

Yeah, the issue is that jsdom is missing TextEncoder (but does have Uint8Array). You're pulling TextEncoder in from util which is a node library not meant to run in a browser environment.

nodejs/node#31852 would also fix your instanceof issue, but the main problem here is that you're trying to mix Node realm into the JSDOM (vm) realm.

---

If you really want to check the type in the test, you can use https://nodejs.org/api/util.html#utiltypesisuint8arrayvalue which works cross-realm.

diff --git i/index.spec.js w/index.spec.js
index 477703f..491cb60 100644
--- i/index.spec.js
+++ w/index.spec.js
@@ -2,5 +2,5 @@ const util = require("util");
 
 test("repro", async () => {
   const encoder = new util.TextEncoder();
-  expect(encoder.encode("€")).toBeInstanceOf(Uint8Array);
+  expect(util.types.isUint8Array(encoder.encode("€"))).toBe(true);
 });

This works for both node and jsdom envs.

[Janpot]

Yep, thank you!

If you really want to check the type in the test

Not really, another library crashed on Uint8Array not being the node.js implementation. I ultimately took a step back and sorted out polyfilling the jsdom environment differently (as custom testEnvironment and not in setupFilesAfterEnv). That way the node environment doesn't get tainted as well.

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