✍️ Chapter 3 — Writing and Running TypeScript

You’ve installed TypeScript, Node.js, and Deno — awesome!
Now let’s write your first TypeScript file and run it, step by step.

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🧠 What is TypeScript?

TypeScript is a language that builds on JavaScript by adding types.
This helps you:

• catch bugs early 🐛
• understand code better 🧠
• work in teams more safely 🤝

You write .ts files, then run them using Deno, or Node.js + a tool like tsx.

📘 Official doc: https://www.typescriptlang.org/docs

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✨ Your first TypeScript file

Step 1 — Create a new folder

mkdir ts-demo
cd ts-demo

Step 2 — Create a file

touch hello.ts

Open it in VS Code:

code .

Paste this code in hello.ts:

function greet(name: string): string {
  return `Hello, ${name}!`;
}

console.log(greet("World"));

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▶️ Option 1: Run it with Deno (no config)

📘 Official Deno site: https://deno.land

Deno runs .ts files directly.

deno run hello.ts

If Deno asks for permission, use:

deno run --allow-read hello.ts

Expected output:

Hello, World!

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▶️ Option 2: Run it with Node.js + tsx

📘 TSX (by esbuild): https://github.com/esbuild-kit/tsx

By default, Node.js can’t run .ts files. But with tsx, you can run TypeScript without compiling manually.

🔧 Step 1 — Install tsx

npm install -g tsx

This installs it globally for your system or your current Node version (if using nvm).

▶️ Step 2 — Run your file

tsx hello.ts

🎉 That’s it! You’re running TypeScript directly in Node.

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⛔ Option 3: Using tsc + node (classic way)

📘 TypeScript CLI docs: https://www.typescriptlang.org/docs/handbook/compiler-options.html

To compile and run manually:

tsc hello.ts     # creates hello.js
node hello.js    # runs the compiled JS file

This approach is more common in large projects, but for now, tsx is easier.

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🧠 Summary

Tool	Description
deno run	Run .ts files directly (built-in support)
tsx	Run .ts files with Node.js (no build step)
tsc + node	Manual build & run (less practical)

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🛠 More docs (optional reading)

• TypeScript Handbook: https://www.typescriptlang.org/docs/handbook/intro.html
• Deno Manual: https://deno.land/manual
• TSX project on GitHub: https://github.com/esbuild-kit/tsx

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✅ You’re ready for the next step

Now let’s learn how TypeScript’s type system works, and why it makes your code more robust and easier to maintain.

👉 Go to Chapter 4: Understanding TypeScript Types