panic when using jest, jsdom and TextEncoder

[Janpot]

Minimal reproduction repo: https://github.com/Janpot/jest-esbuild-repro

Running esbuild in jest with this particular TextEncoder, textDecoder polyfill setup started breaking from [email protected] onward.

To reproduce, clone the repo, run yarn && yarn test. It will error with

 FAIL  ./index.spec.js
  ✕ repro (18 ms)

  ● repro

    panic: interface conversion: interface {} is map[string]interface {}, not []uint8

    debug.Stack (runtime/debug/stack.go:24)
    helpers.PrettyPrintedStack (internal/helpers/stack.go:9)
    main.(*serviceType).handleIncomingPacket.func1 (cmd/esbuild/service.go:220)
    panic (runtime/panic.go:884)
    main.(*serviceType).handleTransformRequest (cmd/esbuild/service.go:923)
    main.(*serviceType).handleIncomingPacket (cmd/esbuild/service.go:236)
    main.runService.func3 (cmd/esbuild/service.go:163)
    created by main.runService (cmd/esbuild/service.go:162)

      at node_modules/esbuild/lib/main.js:1400:29

Test Suites: 1 failed, 1 total
Tests:       1 failed, 1 total
Snapshots:   0 total
Time:        0.41 s, estimated 1 s

The README contains a few of the tweaks that all make the error go away.

environment: node v16.17.0 on MacOs

[evanw]

It's trivial to break esbuild by running it in a broken JavaScript environment. This is not surprising, and does not indicate a problem with esbuild. You can get a similar error by running this code in node without Jest, for example:

global.TextEncoder = class { encode = x => x }
const esbuild = require('esbuild')
esbuild.transform('1+2').then(x => console.log(x))

The support code for esbuild relies on a sane and functioning TextEncoder object. In Jest's case, it seems to have a bug where new TextEncoder().encode() instanceof Uint8Array is incorrectly false. They should fix their bug.

Edit: Or maybe you have written the bug yourself in jest-setup.js? I'm not sure; I know nothing about Jest. Anyway this problem is not esbuild's doing.

[evanw]

Closing as out of scope. In a future breaking change, I could have esbuild do a sanity check for this edge case and throw an error earlier if this API is broken.

[Janpot]

Thank you for taking the time, this helped me narrow down the issue further jestjs/jest#13227

[evanw]

FWIW something like this seems to work:

const util = require("util");

if (!global.TextDecoder) {
  global.TextDecoder = util.TextDecoder;
}

if (!global.TextEncoder) {
  global.TextEncoder = class extends util.TextEncoder {
    encode(text) {
      return new Uint8Array(super.encode(text));
    }
  };
}

In case you're still working on this.

[Janpot]

Yes, thank you. I considered it, but ultimately the test that triggered this issue shouldn't have been using the jsdom environment at all. I just made sure it uses the correct environment and that solves it as well.