TypeScript + Fully-Specified ESM import fails in cy.task

[karlhorky]

Current behavior

Using cy.task fails when it is used along with TypeScript code which uses fully-specified ESM imports (imports using .js extension, where there is no matching .js file because all of the files are TypeScript files , see microsoft/TypeScript#41887 (comment)).

For example:

// website/cypress/plugins/index.ts
import { deleteUserByEmail } from '../../../database/queries/users';

export default function pluginConfig(on: Cypress.PluginEvents) {
  on('task', {
    async deleteUser(email) {
      return await deleteUserByEmail(email);
    },
  });
}

// database/queries/users.ts
import {sql} from '../util/connect.js'

// database/util/connect.ts
export async function sql() {}

Note the difference in file names above. As per microsoft/TypeScript#41887 (comment), this should work in TypeScript (already works when using tsc)

Error message:

  1) Employer sign up
       should sign up with new company and verify email:
     CypressError: `cy.task('deleteEmployer')` failed with the following error:

> Cannot find module '../util/connect.js'
Require stack:
- /Users/lukas/Documents/project/packages/database/queries/users.ts
- /Users/lukas/Documents/project/packages/website/cypress/plugins/index.ts
- /Users/lukas/Library/Caches/Cypress/9.5.1/Cypress.app/Contents/Resources/app/packages/server/lib/plugins/child/run_plugins.js
- /Users/lukas/Library/Caches/Cypress/9.5.1/Cypress.app/Contents/Resources/app/packages/server/lib/plugins/child/index.js

https://on.cypress.io/api/task
      at http://localhost:3020/__cypress/runner/cypress_runner.js:162240:78
      at tryCatcher (http://localhost:3020/__cypress/runner/cypress_runner.js:13022:23)
      at Promise._settlePromiseFromHandler (http://localhost:3020/__cypress/runner/cypress_runner.js:10957:31)
      at Promise._settlePromise (http://localhost:3020/__cypress/runner/cypress_runner.js:11014:18)
      at Promise._settlePromise0 (http://localhost:3020/__cypress/runner/cypress_runner.js:11059:10)
      at Promise._settlePromises (http://localhost:3020/__cypress/runner/cypress_runner.js:11135:18)
      at _drainQueueStep (http://localhost:3020/__cypress/runner/cypress_runner.js:7729:12)
      at _drainQueue (http://localhost:3020/__cypress/runner/cypress_runner.js:7722:9)
      at Async.../../node_modules/bluebird/js/release/async.js.Async._drainQueues (http://localhost:3020/__cypress/runner/cypress_runner.js:7738:5)
      at Async.drainQueues (http://localhost:3020/__cypress/runner/cypress_runner.js:7608:14)
  From Your Spec Code:
      at Context.eval (http://localhost:3020/__cypress/tests?p=cypress/integration/employerSignUp.spec.ts:188:10)
  
  From Node.js Internals:
    Error: Cannot find module '../util/connect.js'
    Require stack:
    - /Users/lukas/Documents/project/packages/database/queries/users.ts
    - /Users/lukas/Documents/project/packages/website/cypress/plugins/index.ts
    - /Users/lukas/Library/Caches/Cypress/9.5.1/Cypress.app/Contents/Resources/app/packages/server/lib/plugins/child/run_plugins.js
    - /Users/lukas/Library/Caches/Cypress/9.5.1/Cypress.app/Contents/Resources/app/packages/server/lib/plugins/child/index.js
        at Function.Module._resolveFilename (node:internal/modules/cjs/loader:933:15)
        at Function.Module._load (node:internal/modules/cjs/loader:778:27)
        at Module.require (node:internal/modules/cjs/loader:999:19)
        at require (node:internal/modules/cjs/helpers:102:18)
        at Object.<anonymous> (/Users/lukas/Documents/project/packages/database/queries/users.ts:5:1)
        at Module._compile (node:internal/modules/cjs/loader:1097:14)
        at Module.m._compile (/Users/lukas/Library/Caches/Cypress/9.5.1/Cypress.app/Contents/Resources/app/node_modules/ts-node/src/index.ts:607:4)
        at Module._extensions..js (node:internal/modules/cjs/loader:1149:10)
        at Object.require.extensions.<computed> [as .ts] (/Users/lukas/Library/Caches/Cypress/9.5.1/Cypress.app/Contents/Resources/app/node_modules/ts-node/src/index.ts:610:10)
        at Module.load (node:internal/modules/cjs/loader:975:32)
        at Function.Module._load (node:internal/modules/cjs/loader:822:12)
        at Module.require (node:internal/modules/cjs/loader:999:19)
        at require (node:internal/modules/cjs/helpers:102:18)
        at /Users/lukas/Documents/project/packages/website/cypress/plugins/index.ts:30:37
        at processTicksAndRejections (node:internal/process/task_queues:96:5)
        at deleteEmployer (/Users/lukas/Documents/project/packages/website/cypress/plugins/index.ts:30:37)

Desired behavior

Fully-specified ESM imports using .js file extensions should work in TypeScript code

Two details:

1. This will be fixed in one of the coming versions of ts-node feat(register): resolve .js to .ts in ts-node/register TypeStrong/ts-node#1361
2. An old 8.5.4 version of ts-node is currently used in the macOS Cypress.app via the server package (apparently? I was surprised to find it there):

   cypress/packages/server/package.json

   Line 115 in 024308b

   "ts-node": "8.5.4",

Test code to reproduce

See above

Cypress Version

9.5.1

Other

It would be nice if Cypress also supported Node.js ESM code just generally, but I think there are other issues for that:

• Error [ERR_REQUIRE_ESM]: Must use import to load ES Module error thrown #8090
• CJS plugins file (and ideally also allowing an ESM one) #16467

[karlhorky]

Workaround: precompile the TypeScript files to CJS (run tsc using "module": "CommonJS")

[spiffytech]

ts-node 10.8.0 has been released with .js extension resolution. Would that resolve this for Cypress?

I'm interested in a workaround that doesn't target CommonJS; my project is ESM and I'd like to have Cypress tasks import my app code.

[karlhorky]

Yeah, it would be great to have ESM support in Cypress.

I don't think new versions of ts-node will be helpful - it has had ESM support for quite a few versions. The problem is the very old version of ts-node inside of the macOS app Cypress.app (I imagine, also the Electron apps for Windows and Linux). It will need to be updated.

[karlhorky]

Ah, looks like Cypress v10 has updated this ts-node in the server package!

cypress/packages/server/package.json

Line 120 in a0a64cc

"ts-node": "^10.2.1",

Maybe fully-specified ESM imports will work now... 🤔

[karlhorky]

Everything is working now with the recent "type": "module" fix by @lmiller1990 (released in cypress@10.1.0).

To take advantage of this, make sure that you have:

1. "type": "module" in the package where your cypress.config.ts is
2. Fully-specified imports using the .js file extension (see below)

cypress.config.ts

import { defineConfig } from 'cypress';
-import * as users from './database/queries/users';
+import * as users from './database/queries/users.js';

export default defineConfig({
  e2e: {
    setupNodeEvents(on) {
      on('task', {
        async deleteUserByEmail(email: string) {
          return (await users.deleteUserByEmail(email)) || null;
        },
      });
    },
  },
});

[lmiller1990]

Alternatively, change your .js files to .ts - not always an option, but when it is, you won't need the extension. CJS + ESM interop is such a mess right now (not specifically here, but in the entire ecosystem...).

As an aside, you have no idea how good it feels to get a notification in an already closed issue that actually clarifies things are working and provides useful info for future users! Thank you for this!

[karlhorky]

Alternatively, change your .js files to .ts - not always an option, but when it is, you won't need the extension

This is not true with TypeScript and fully-specified imports in ESM, check out microsoft/TypeScript#41887 (comment)

The files associated with the .js paths are already written in TypeScript (the files already have a .ts extension). In the import path, the correct way is to write a .js extension for these .ts files.

As an aside, you have no idea how good it feels to get a notification in an already closed issue that actually clarifies things are working and provides useful info for future users! Thank you for this!

Great, really good to hear! 😃 I've been trying to open issues and post solutions to clear up some of the confusion around ESM + TS interop.

[lmiller1990]

Right, so, if I want to use native ESM in my TS files, I actually need to do js in the import (even when importing a ts file? Or is this only to import a ESM js file into a ESM ts file?

I will need to play with this more. I've been using type: module and module: esnext but haven't imported JS into TS before - my understanding is in that case I need JS, but if all my files are ts, I don't?

[karlhorky]

if I want to use native ESM in my TS files, I actually need to do js in the import (even when importing a ts file?

Yep, counterintuitive but true.