Ecosystem & Toolchain

Running TypeScript in Node.js

TypeScript is not natively understood by Node.js — it must be stripped or compiled first. You have three main options in the modern ecosystem:

Option 1: `--experimental-strip-types` (Node 20.6+ / stable Node 22)

Node can strip TypeScript type annotations at startup without any extra package. It does not type-check — it just removes the types and runs the JavaScript:

# Node 22 — stable
node --experimental-strip-types src/app.ts

# Node 20.6+
node --experimental-strip-types --input-type=module src/app.ts

Limitations: no enum, no namespace, no experimentalDecorators. For those, use tsx or ts-node.

Option 2: tsx — fast TypeScript runner

tsx is a lightweight wrapper around esbuild. It handles all TypeScript features and starts in milliseconds:

# Run once
npx tsx src/app.ts

# Watch mode — auto-restart on changes
npx tsx watch src/app.ts

# Install as a dev dependency
npm install --save-dev tsx

Option 3: ts-node — the classic

ts-node has been the standard for years. It is heavier than tsx but has mature configuration support:

npm install --save-dev ts-node typescript

# Run a file
npx ts-node src/app.ts

# ESM mode (tsconfig must have "module": "NodeNext")
npx ts-node --esm src/app.ts

Linters and Formatters

ESLint — catch logic errors and enforce style rules

# Install ESLint with TypeScript support
npm install --save-dev eslint @eslint/js typescript-eslint

# Create a flat config (eslint.config.mjs)
# then run:
npx eslint src/

# Auto-fix fixable issues
npx eslint --fix src/

A minimal eslint.config.mjs for TypeScript:

import js from '@eslint/js';
import tseslint from 'typescript-eslint';

export default tseslint.config(
  js.configs.recommended,
  ...tseslint.configs.recommended,
);

Prettier — opinionated code formatter

npm install --save-dev prettier

# Format all files
npx prettier --write .

# Check formatting without changing files (for CI)
npx prettier --check .

Prettier and ESLint focus on different things: Prettier handles formatting (spacing, quotes, semicolons), ESLint handles logic and style rules. Run both in sequence or use eslint-config-prettier to disable ESLint’s formatting rules.

Biome — one tool for both lint and format

Biome replaces ESLint + Prettier with a single fast tool written in Rust:

npm install --save-dev @biomejs/biome
npx biome init

# Lint and format in one pass
npx biome check --apply src/

Watch Mode and nodemon

Node built-in watch (Node 18+)

# Restart on any file change — no install required
node --watch src/app.js

# Watch specific files
node --watch-path=src src/app.js

nodemon — battle-tested watcher

npm install --save-dev nodemon

# Basic usage
npx nodemon src/app.js

# With TypeScript via tsx
npx nodemon --exec "npx tsx" src/app.ts

# nodemon.json config

{
  "watch": ["src"],
  "ext": "ts,js,json",
  "exec": "npx tsx src/app.ts"
}

Environment Variables and .env Files

Native .env loading (Node 20.6+)

# Load a .env file without dotenv
node --env-file=.env src/app.js

# Load multiple env files (later files override earlier)
node --env-file=.env --env-file=.env.local src/app.js

dotenv — the classic

npm install dotenv

// src/app.js — load at the very top
import 'dotenv/config';

console.log(process.env.DATABASE_URL); // from .env

Best practices for env files

# .env — default values, committed to git (no secrets)
NODE_ENV=development
PORT=3000
LOG_LEVEL=info

# .env.local — local overrides, NOT committed (in .gitignore)
DATABASE_URL=postgres://localhost:5432/mydb
SECRET_KEY=dev-only-secret

# .env.example — template showing required vars, committed
DATABASE_URL=
SECRET_KEY=

Always add .env.local and .env*.local to .gitignore. Never commit real secrets.

package.json scripts — the glue

{
  "scripts": {
    "dev": "tsx watch src/app.ts",
    "build": "tsc --noEmit",
    "start": "node dist/app.js",
    "test": "node --test",
    "lint": "eslint src/ && prettier --check .",
    "format": "prettier --write . && eslint --fix src/"
  }
}