Always overriding global value breaks some tests

[jlowcs]

I have a suggestion to improve the current implementation and to avoid issues like #32 and other similar issues (e.g. I have one related to Blob).

const JSDOMEnvironment = require('jest-environment-jsdom').default

class FixedJSDOMEnvironment extends JSDOMEnvironment {
  constructor(...args) {
    super(...args)

    /**
     * @note Opt-out from JSDOM using browser-style resolution
     * for dependencies. This is simply incorrect, as JSDOM is
     * not a browser, and loading browser-oriented bundles in
     * Node.js will break things.
     *
     * Consider migrating to a more modern test runner if you
     * don't want to deal with this.
     */
    this.customExportConditions = args.customExportConditions || ['']

    setIfNonDefined.call(this, 'TextDecoder', TextDecoder)
    setIfNonDefined.call(this, 'TextEncoder', TextEncoder)
    setIfNonDefined.call(this, 'TextDecoderStream', TextDecoderStream)
    setIfNonDefined.call(this, 'TextEncoderStream', TextEncoderStream)
    setIfNonDefined.call(this, 'ReadableStream', ReadableStream)

    setIfNonDefined.call(this, 'Blob', Blob)
    setIfNonDefined.call(this, 'Headers', Headers)
    setIfNonDefined.call(this, 'FormData', FormData)
    setIfNonDefined.call(this, 'Request', Request)
    setIfNonDefined.call(this, 'Response', Response)
    setIfNonDefined.call(this, 'fetch', fetch)
    setIfNonDefined.call(this, 'structuredClone', structuredClone)
    setIfNonDefined.call(this, 'URL', URL)
    setIfNonDefined.call(this, 'URLSearchParams', URLSearchParams)

    setIfNonDefined.call(this, 'BroadcastChannel', BroadcastChannel)
    setIfNonDefined.call(this, 'TransformStream', TransformStream)
  }
}

function setIfNonDefined(key, value) {
	if (!this.global[key]) {
		this.global[key] = value
	}
}

module.exports = FixedJSDOMEnvironment