[ERR_UNKNOWN_FILE_EXTENSION]: Unknown file extension ".ts"

[abhinavsingh]

This is how I led to conclusion that above error is related to fetch-mock.

1. I recently got a new laptop. Default node installed by brew is v18.6.0, compared to previous v17.x on my older system
2. Upgrading node resulted in some caveats e.g. usage of NODE_OPTIONS=--no-experimental-fetch became necessary for rpm run build in some of our repos.
3. Coming to tests, we observed below stack trace in some of our repos

TypeError [ERR_UNKNOWN_FILE_EXTENSION]: Unknown file extension ".ts" for /Users/abhinavsingh/Dev/....redacted..../tests/payments.ts
    at new NodeError (node:internal/errors:387:5)
    at Object.getFileProtocolModuleFormat [as file:] (node:internal/modules/esm/get_format:80:11)
    at defaultGetFormat (node:internal/modules/esm/get_format:122:38)
    at defaultLoad (node:internal/modules/esm/load:81:20)
    at nextLoad (node:internal/modules/esm/loader:173:28)
    at ESMLoader.load (node:internal/modules/esm/loader:616:26)
    at ESMLoader.moduleProvider (node:internal/modules/esm/loader:472:22)
    at new ModuleJob (node:internal/modules/esm/module_job:63:26)
    at ESMLoader.#createModuleJob (node:internal/modules/esm/loader:491:17)
    at ESMLoader.getModuleJob (node:internal/modules/esm/loader:449:34)
    at async Promise.all (index 0)
    at async ESMLoader.import (node:internal/modules/esm/loader:541:24)
    at async importModuleDynamicallyWrapper (node:internal/vm/module:438:15)
    at async formattedImport (/Users/abhinavsingh/Dev/....redacted..../node_modules/mocha/lib/nodejs/esm-utils.js:7:14)

4. Going into payments.ts, as soon as we comment out const fetchMock = require('fetch-mock');, error goes away. We saw similar behaviour for all our tests using fetch-mock
5. I went to https://www.npmjs.com/package/fetch-mock in hope of a newer version, but found none.
6. I tried NODE_OPTIONS=--no-experimental-fetch with npm test, but run into same exception.

Dependency list:

    "@types/chai": "^4.3.0",
    "@types/mocha": "^9.1.0",
    "@types/node-fetch": "^2.6.2",
    "chai": "^4.3.6",
    "fetch-mock": "^9.11.0",
    "gulp": "^4.0.2",
    "gulp-typescript": "^6.0.0-alpha.1",
    "jsdom": "^20.0.0",
    "jsdom-global": "^3.0.2",
    "mocha": "^10.0.0",
    "node-fetch": "^3.2.9",
    "nyc": "^15.1.0",
    "ts-node": "^10.9.1",
    "typedoc": "^0.23.9"

Any help and/or pointers are appreciated. Best

[agustin-del-pino]

Hello, same error from here.

TypeError [ERR_UNKNOWN_FILE_EXTENSION]: Unknown file extension ".ts" for /workspaces/test/a.super.good.test.ts
    at new NodeError (node:internal/errors:371:5)
    at Object.getFileProtocolModuleFormat [as file:] (node:internal/modules/esm/get_format:87:11)
    at defaultGetFormat (node:internal/modules/esm/get_format:102:38)
    at defaultLoad (node:internal/modules/esm/load:21:14)
    at ESMLoader.load (node:internal/modules/esm/loader:359:26)
    at ESMLoader.moduleProvider (node:internal/modules/esm/loader:280:58)
    at new ModuleJob (node:internal/modules/esm/module_job:66:26)
    at ESMLoader.#createModuleJob (node:internal/modules/esm/loader:297:17)
    at ESMLoader.getModuleJob (node:internal/modules/esm/loader:261:34)
    at async Promise.all (index 0)
    at async ESMLoader.import (node:internal/modules/esm/loader:337:24)
    at async importModuleDynamicallyWrapper (node:internal/vm/module:437:15)
    at async formattedImport (/workspaces/node_modules/mocha/lib/nodejs/esm-utils.js:7:14)
    at async Object.exports.requireOrImport (/workspaces/node_modules/mocha/lib/nodejs/esm-utils.js:38:28)
    at async Object.exports.loadFilesAsync (/workspaces/node_modules/mocha/lib/nodejs/esm-utils.js:91:20)
    at async singleRun (/workspaces/node_modules/mocha/lib/cli/run-helpers.js:125:3)
    at async Object.exports.handler (/workspaces/node_modules/mocha/lib/cli/run.js:370:5)

{
  "scripts": {
    "test": "env TS_NODE_COMPILER_OPTIONS='{\"module\": \"commonjs\"}' mocha -r ts-node/register 'tests/**/*.ts'"
  },
  "devDependencies": {
    "@types/chai": "^4.3.1",
    "@types/fetch-mock": "^7.3.5",
    "@types/mocha": "^9.1.1",
    "chai": "^4.3.6",
    "chai-fetch-mock": "^3.0.0",
    "mocha": "^10.0.0",
    "node-fetch": "^3.2.9",
    "ts-node": "^10.9.1",
    "typescript": "^4.7.4"
  }
}

The exception never occurs when the line fetchMock.mock(...); is commented.