// A taste of TypeScript

// An interface is a contract: any object claiming to be a "User"
// MUST have exactly these properties with these types.
interface User {
  id: number;
  name: string;
  email: string;
  role: 'admin' | 'user' | 'guest'; // Union type: only these 3 strings are allowed
}

// Parameter types and return types are explicit -- no guessing what this function expects
function greetUser(user: User): string {
  return `Hello, ${user.name}! You are logged in as ${user.role}.`;
}

// TypeScript checks this object against the User interface at compile time.
// Missing a property? Wrong type? You will know before the code ever runs.
const user: User = {
  id: 1,
  name: 'Alice',
  email: 'alice@example.com',
  role: 'admin'
};

console.log(greetUser(user)); // "Hello, Alice! You are logged in as admin."

# Install globally
npm install -g typescript

# Check version
tsc --version

# Initialize a project
tsc --init

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

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

# Compile to JavaScript
tsc hello.ts

# Run the compiled JS
node hello.js

# Install ts-node
npm install -g ts-node

# Run TypeScript directly
ts-node hello.ts