1. I created a new Node.js project with Node version 18.15.0. In the package.json, I added the field “type”: “module”.

{
  "name": "ts-node-test",
  "version": "1.0.0",
  "description": "",
  "type": "module",
  "scripts": {
    "test": "cross-env NODE_OPTIONS="--loader ts-node/esm" node index.cts"
  },
  "author": "",
  "license": "ISC",
  "devDependencies": {
    "cross-env": "^7.0.3",
    "ts-node": "^10.9.2",
    "tslib": "^2.6.2",
    "typescript": "^5.4.5"
  },
  "volta": {
    "node": "18.15.0"
  }
}

2. The config of tsconfig.json is:

{
  "$schema": "https://json.schemastore.org/tsconfig",
  "ts-node": {
    "transpileOnly": true,
    "files": true,
    "experimentalResolver":true,
    "esm": true,
  },
  "compilerOptions": {
    "outDir": "./dist",
    "allowJs": true,
    "allowSyntheticDefaultImports": true,
    "baseUrl": "./",
    "esModuleInterop": true,
    "experimentalDecorators": true,
    "forceConsistentCasingInFileNames": true,
    "importHelpers": true,
    "lib": [
      "DOM",
      "ESNext"
    ],
    "module": "ESNext",
    "moduleDetection": "force",
    "moduleResolution": "node",
    "noEmitOnError": true,
    "resolveJsonModule": true,
    "skipLibCheck": true,
    "sourceMap": true,
    "strict": true,
    "target": "esnext",
    "typeRoots": [
      "./node_modules/@types",
    ]
  },
  "include": [
    "index.cts",
    "module.cts"
  ]
}

3. I created a new file named index.cts with the following code:

import test from './module.cjs'

console.log(test(1, 2))

4. In the same folder, the code of the file module.cts is:

export default (a: number, b: number) => a + b

5. Afterward, I executed the script “test”, which produced the result without any errors.

3

It seems that .cts extension in Node.js can use module syntax for imports and exports.
why?

6. The complete project information has been uploaded to GitHub. The GitHub repository can be found at: https://github.com/yaotusa/ts-node-test