make jsdom accessible to extending environments

[robin-drexler]

Fixes: #12233

I initially wanted to create an issue, but thought it may be better if I opened a PR. Please let me know if you'd rather have me open an issue.

In f9814d2 dom has been made private.

This causes extending environments that depend on this.dom being available like jest-environment-jsdom-global to break if they use TypeScript.

The error you get if you try to access this.dom in an environment:

 Property 'dom' is private and only accessible within class 'JSDOMEnvironment'.

export class JSDOMEnvironmentGlobal extends JSDOMEnvironment {
  constructor(config, options) {
    super(config, options);

   // this line triggers the error
    this.global.jsdom = this.dom;
  }
}

I prepared a small reproduction repository.
It uses a custom TS environment that tries to access this.dom and fails.

To see for yourself:

• clone the repo
• run npm install
• run npx jest

jest-environment-jsdom-global itself is actually unaffected because it uses JS and the transpiled CommonJS version of jest-environment-jsdom doesn't enforce this.dom to be private. If jest changes its bundling process in the future, this could also fail for projects using JS.

I think it'd be great if jsdom continued to be accessible for custom environments since that enables use cases that would otherwise not be possible.

[robin-drexler]

I guess that would introduce whatever the previous PR fixed. I'll create an issue instead first.

[SimenB]

thanks!

you also need to move https://github.com/facebook/jest/blob/df0c496fa2b39293c26967f66bada30c3dcfd3c4/packages/jest-environment-jsdom/package.json#L30 to dependencies and add a changelog entry 🙂

[SimenB]

thanks!

[robin-drexler]

@SimenB thanks for the guidance and review! 🙌

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