[Feature] Support TypeScript declare fields, and/or consult tsconfig target or useDefineForClassFields

[mweidner037]

In some Playwright Test TypeScript code, I need to declare the TypeScript type of a class's field without defining the field in JS (due to a library). The TypeScript docs describe a few ways to do this:

1. Change the tsconfig target to < es2022
2. Set the tsconfig useDefineForClassFields to false
3. Use declare on the class fields, e.g.,

class TestClass {
  public declare x: number;
}

However, I have not gotten any of these to work in Playwright Test (MWE repo):

• tsconfig target and useDefineForClassFields are apparently not consulted by Playwright Test (they do work with ts-node).
• Running the code snippet above within Playwright Test fails with:

Error: /Users/matthew/repos/playwright-test-mwes/tests/declare_fields.test.ts: TypeScript 'declare' fields must first be transformed by @babel/plugin-transform-typescript.
If you have already enabled that plugin (or '@babel/preset-typescript'), make sure that it runs before any plugin related to additional class features:
 - @babel/plugin-proposal-class-properties
 - @babel/plugin-proposal-private-methods
 - @babel/plugin-proposal-decorators
  2 |
  3 | class TestClass {
> 4 |   public declare x: number;
    |   ^^^^^^^^^^^^^^^^^^^^^^^^^
  5 | }
  6 |
  7 | test('declare_fields', async ({ page }) => {

Note this is in a project with no Babel setup - it appears to reference playwright's internal Babel. Adding a babel.config.json with @babel/plugin-transform-typescript doesn't fix the error.

Playwright Test version: 1.24.2.

[mxschmitt]

Playwright does not respect the tsconfig target nor the babel config. For more advanced setups we recommend compiling the TypeScript tests manually see this guide: https://playwright.dev/docs/test-typescript#manually-compile-tests-with-typescript

We can keep this feature request open, if enough customers request it, we can add it by default.

[jparr]

As another Sequelize user this would be really useful. Currently to seed the database I am shelling out to call an npm script in beforeEach which adds about 12 seconds to each test.

[pavelfeldman]

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