Fix: ERR_UNKNOWN_FILE_EXTENSION '.ts' error

The ‘ERR_UNKNOWN_FILE_EXTENSION .ts’ error occurs when Node.js cannot recognize the ‘.ts’ file extension, typically because it doesn’t know how to handle TypeScript files without proper configuration or transpilation.

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How the Error Happens

❌ Error Scenario:

# ❌ This causes the error
node src/index.ts
# Error: ERR_UNKNOWN_FILE_EXTENSION .ts

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✅ Quick Fix - Handle TypeScript in Node.js

Solution 1: Use ts-node for Development

# ✅ Install ts-node globally or locally
npm install -g ts-node
# OR for local project
npm install --save-dev ts-node

# ✅ Run TypeScript files directly
npx ts-node src/index.ts
# OR if installed globally
ts-node src/index.ts

Solution 2: Transpile to JavaScript First

# ✅ Install TypeScript compiler
npm install -g typescript
# OR for local project
npm install --save-dev typescript

# ✅ Create tsconfig.json
{
  "compilerOptions": {
    "target": "ES2020",
    "module": "commonjs",
    "outDir": "./dist",
    "rootDir": "./src",
    "strict": true,
    "esModuleInterop": true
  }
}

# ✅ Compile TypeScript to JavaScript
tsc

# ✅ Run the compiled JavaScript
node dist/index.js

Solution 3: Use tsx for Modern Execution

# ✅ Install tsx (faster TypeScript execution)
npm install -g tsx
# OR for local project
npm install --save-dev tsx

# ✅ Run TypeScript files directly with tsx
npx tsx src/index.ts
# OR if installed globally
tsx src/index.ts

Solution 4: Configure Package.json for TypeScript

// ✅ Add to package.json
{
  "name": "my-app",
  "type": "module",
  "scripts": {
    "dev": "tsx watch src/index.ts",
    "start": "tsx src/index.ts",
    "build": "tsc"
  },
  "devDependencies": {
    "tsx": "^4.0.0",
    "typescript": "^5.0.0"
  }
}

// ✅ For ES modules with .ts files, use loader
node --loader ts-node/esm src/index.ts