ERR_UNKNOWN_FILE_EXTENSION for tsconfig.json esm:true / NODE_OPTIONS works

[zirkelc]

Search Terms

ESM
NODE_OPTIONS
TypeError [ERR_UNKNOWN_FILE_EXTENSION]: Unknown file extension ".ts"

Expected Behavior

I'm using ts-node as part of Serverless to read the serverless.ts configuration file in my project which is defined as ESM with "type": "module" in package.json and "esm": true in tsconfig.json.

Same behavior like NODE_OPTIONS="--loader ts-node/esm".

Actual Behavior

If I start the serverless CLI with NODE_OPTIONS="--loader ts-node/esm", it loads the serverless.ts without a problem. However, if I avoid the NODE_OPTIONS env, I get the following error:

TypeError [ERR_UNKNOWN_FILE_EXTENSION]: Unknown file extension ".ts"

ts-node is used programmatically and registered as require(tsNodePath).register(); and I can verify that the tsNodePath points to a locally installed package. Somehow, when it then comes to the following await import('serverless.ts') it crashes with this error.

Steps to reproduce the problem

Minimal reproduction

See repo: https://github.com/zirkelc/serverless-esm-test

Steps to reproduce:

1. clone repo
2. npm install
3. npx sls package
   throws error ERR_UNKNOWN_FILE_EXTENSION]
4. NODE_OPTIONS="--loader ts-node/esm" npx sls package
   no error

Specifications

ts-node v10.8.1
node v16.13.0
compiler v4.7.3

• tsconfig.json, if you're using one:

{
  "extends": "@tsconfig/node16-strictest-esm/tsconfig.json",
  "compilerOptions": {
    "moduleResolution": "node",
    "sourceMap": true,
    "outDir": "dist",
  },
  "include": [
    "src/**/*.ts",
    "serverless.ts"
  ],
  "exclude": [
    "node_modules/**/*",
    ".serverless/**/*",
    ".webpack/**/*",
    "_warmup/**/*",
    ".vscode/**/*"
  ],
  "ts-node": {
    "esm": true,
  }
}

• package.json:

{
  "name": "serverless-esm-test",
  "version": "1.0.0",
  "description": "Serverless aws-nodejs-typescript template",
  "main": "serverless.ts",
  "type": "module",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1",
    "sls:package": "nodemon --ext ts --exec \"npx sls package\""
  },
  "engines": {
    "node": ">=14.15.0"
  },
  "dependencies": {
    "@middy/core": "^3.0.4",
    "@middy/http-json-body-parser": "^3.0.4"
  },
  "devDependencies": {
    "@serverless/typescript": "^3.18.0",
    "@tsconfig/node16-strictest-esm": "^1.0.1",
    "@types/aws-lambda": "^8.10.98",
    "@types/node": "^17.0.40",
    "esbuild": "^0.14.42",
    "json-schema-to-ts": "^2.5.3",
    "serverless": "github:zirkelc/serverless#add-esm-support-configuration",
    "serverless-esbuild": "^1.30.0",
    "ts-node": "^10.8.1",
    "tsconfig-paths": "^4.0.0",
    "typescript": "^4.7.3"
  },
  "author": "The serverless webpack authors (https://github.com/elastic-coders/serverless-webpack)",
  "license": "MIT"
}

• Operating system and version:
• If Windows, are you using WSL or WSL2?:
  macOS

[cspotcode]

Node does not give us any way to programmatically register the ESM hooks at runtime. If you're curious to learn more, check out node's docs for --loader.

Seems like you do have a working solution with NODE_OPTIONS. As na alternative, some projects choose to write their config as CommonJS, and there are various options for doing that in an otherwise ESM project.