Getting error "TypeError: Unknown file extension" when trying to run a NodeJS application via Type Script and Express

Question

I am trying to run a Node.js application using TypeScript and Express. However, I am encountering the following issues:

When I run npm run dev, I get: TypeError: Unknown file extension '.ts'

When I run ts-node src/app.ts, I get: TypeError: Unknown file extension '.ts'

When I run ts-node dist/app.js, I get: Error: Cannot find module

What I Have Tried:

I have installed all necessary dependencies as listed in my package.json.

Here's my tsconfig

"compilerOptions": {
  "module": "ESNext",
  "target": "ESNext",
  "moduleResolution": "node",
  "esModuleInterop": true,
  "emitDecoratorMetadata": true,
  "experimentalDecorators": true,
  "outDir": "./dist",
  "rootDir": "./src"
}

Here's my nodemon config,

{
  "watch": ["src"],
  "execMap": {
    "ts": "ts-node"
  },
  "ext": "ts",
  "ignore": ["src/**/*.spec.ts"]
}

Here's my package.json,

{
  "name": "Testing",
  "version": "1.0.0",
  "description": "",
  "main": "src/app.ts",
  "type": "module",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1",
    "start": "node dist/app.ts",
    "dev": "nodemon",
    "build": "tsc"
  },
  "dependencies": {
    "dotenv": "^16.4.5",
    "express": "^4.19.2",
    "npm": "^11.0.0",
    "reflect-metadata": "^0.1.13",
    "routing-controllers": "^0.10.4",
    "typeorm": "^0.3.20"
   },
   "devDependencies": {
     "@types/express": "^4.17.21",
     "@types/node": "^20.17.10",
     "@types/request": "^2.48.12",
     "nodemon": "^3.1.9",
     "ts-node": "^10.9.2",
     "typescript": "^5.7.2"
   }
}

Environment:

Node.js version: 20.12.2

npm version: 6.14.11

How can I resolve the errors I am encountering and run my TypeScript and Express application correctly? Are there any issues with my configuration, or am I missing something critical?

Answer 1

This is an example of vanilla-typescript project using Vite: Vite Typescript Vanilla in stackblitz

You may follow the configuration it has, and Im sure your project should work. As a recommendation, I would recommend using tsx: https://tsx.is/

$ npm install tsx -D

and then you can use it on a npm script:

"scripts": {
    "test": "echo \"Error: no test specified\" && exit 1",
    "start": "tsx ./app.ts",
    "dev": "tsx watch ./app.ts",
    "build": "tsc"
  },

---

$ npm run dev

Should work.

Answer 2

How to run TypeScript files from command line?

I think a quick Google search will lead you to this. The TL;DR is that Node.js can understand JavaScript, but not TypeScript.

Use npx ts-node src/foo.ts to convert and run the TypeScript file in one step, or do it in two steps with tsc (the first option is simpler).