Can't use top-level await

🐛 Bug Report

Not sure if I’m doing something wrong, or if TLA isn’t supposed to work due to #1709.

To Reproduce

cd into the cloned repro repo, npm install, npm test.

Expected behavior

The test should pass.

Link to repo (highly encouraged)

https://github.com/dandv/ts-jest-tla

envinfo

System:
    OS: Ubuntu Linux 20

Npm packages:
    jest: 26.6.0
    ts-jest: 26.4.1
    typescript: 4.0.3
    babel(optional): not used

[HerbCaudill]

@mayacoda @brendonco I struggled with this for a bit and finally got it working — see my fork of @dandv’s repo here: https://github.com/HerbCaudill/ts-jest-tla

The key things to make sure of are:

• You need jest and ts-jest version 27 or higher.

• These settings need to be in your Jest config:

  "jest": {
    "preset": "ts-jest/presets/default-esm",
    "globals": {
      "ts-jest": {
        "useESM": true
      }
    }
  }
  

• You need "type": "module" in package.json.

• In tsconfig.json, you need

    "target": "esnext",
    "module": "esnext"
  

  (The top-level await error says that targeting es2017 or higher would work, but only esnext has worked for me.)

• Jest needs to be run with the --experimental-vm-modules flag. For example my test script looks like this:

  "test": "node --no-warnings --experimental-vm-modules node_modules/jest/bin/jest.js"
  

  The --no-warnings flag isn’t strictly necessary, but otherwise you get yelled at on every test run that --experimental-vm-modules is experimental. 🙄

Hope this helps others who run into this.

[mayacoda]

@mayacoda did you manage to test top level await?

I was not able to get it to work with the above described settings, unfortunately.

As for support in TypeScript 4.5, the link @fernandopasik provided also says

This [top-level await] was already supported in --module esnext (and now–module nodenext), but es2022 is the first stable target for this feature.

Which makes me think it should already work with the configuration above and something else is preventing it. Hopefully, I’m wrong and it does get fixed with the new version of TypeScript.