[Feature] Allow tests to be written in typescript with "type": "module" in the absence of a config file

[lilnasy]

In the process of moving from vitest to @playwright/test, I kept running into this issue:

> pnpm playwright test
TypeError: Unknown file extension ".ts" for /workspace/project/tests/basics.spec.ts



Error: No tests found

After browsing around and finding #27827 and #23662 to no help, I realised it was because I did not have playwright.config in my project. I do not want to change any defaults and I certainly don't want another root-level config if I can avoid it.

To reproduce, run npm init playwright with all default options, then remove playwright.config file and add "type": "module" to the package.json.

[dgozman]

@lilnasy Unfortunately, Playwright is not going to support this in the near future. To work with typescript and "type": "module", we need to engage the ESM loader, and we do so when we encounter config that is a module itself. Otherwise, we would have to engage the ESM loader upon reading your test files, which is too late. That said, once ESM loader story in Node.js matures, there might be changes in this area.

[lilnasy]

Could there be an explicit opt-in, similar to node's --experimental-default-type=ts-module? Anything to bypass the implicit heuristics would be valuable.

I personally don't mind the cli flag being long and I could try to implement it if the team is receptive to the idea.

[lilnasy]

Thanks for the pointer! After looking around the codebase, I got it working with this script:

"scripts": {
-   "test": "playwright test"
+   "test": "node --no-warnings --experimental-loader playwright/lib/transform/esmLoader node_modules/playwright/cli.js test"
},

[mxschmitt]

This might be fixed in v1.43.

[lilnasy]

Yes, it has!

Thanks @mxschmitt for implementing ts loader on top of newer node APIs and the shout. Thanks @dgozman for flipping the switch.

• Fixed by fix(esm): >= Node.js 21 globalPreload -> initialize #28526 followed by feat: always enable ESM loader with the new API #29991.