CODEWITHSUNDEEP
typescriptjestjsnext.jsweb-workerswc-compiler
Maxe
Maxe

Reputation: 113

Jest: How to transform import.meta.url using Next 12 with SWC

I am using Jest in a Next.js 12 App with the Rust Compiler.
Since I'm using WebWorkers I have a file in which I use import.meta.url. to construct the worker

The problem with that is, that Jest will throw an error stating I can't use import.meta.url outside an ES Module (Since it still transforms the typescript code to commonJs) I saw that one could add a babel plugin which would then transform those files which include import.meta.url. https://github.com/facebook/jest/issues/12183#issuecomment-1004320665

But I would prefer not using Babel, since I use the Jest config from Next which is using the rust compiler. Also I am not sure if I can even use this babel plugin in this configuration.

I also know that one could configure jest to use ESModules instead but I don't want to use this method either since it's experimental and produces some strange errors in my project.
So I want to know: Is there a way (or better a SWC plugin) to use this transformation with SWC?

Upvotes: 5

Views: 2895

Answers (1)

Todd
Todd

Reputation: 972

A solution that doesn't require massive changes to the application or testing configuration is to refactor the import.meta.url call into a helper module, and when testing the original file, mock the helper module. Here's the general idea.

// my-module.js
import { importMetaUrl } from './import-meta-url'
export function foo() {
   return importMetaUrl()
}


// import-meta-url.js
export function importMetaUrl() {
  return import.meta.url
}

// my-module.test.js
import { foo } from './my-module'

jest.mock('./import-meta-url', () => ({
   importMetaUrl: () => 'http://www.example.org'
})

test('test', () => {
  expect(foo()).toEqual('http://www.example.org')
})

Upvotes: 0

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