What is TypeScript?

TypeScript is a strongly typed superset of JavaScript that compiles to plain JavaScript. Developed and maintained by Microsoft, it adds optional static typing and class-based object-oriented programming to the language.

Why TypeScript?

• Type Safety: Catch errors at compile time, not runtime
• Better IDE Support: Autocompletion, refactoring, navigation
• Self-Documenting: Types serve as inline documentation
• Scalability: Easier to maintain large codebases
• JavaScript Compatibility: All JavaScript is valid TypeScript

How TypeScript Works:

1. Write TypeScript code (.ts files)
2. TypeScript compiler checks for type errors
3. Compiles to plain JavaScript
4. JavaScript runs in any environment

TypeScript doesn't run directly - it's always compiled to JavaScript first. This means there's no runtime type checking, only compile-time.

// Type annotations
let message: string = "Hello, TypeScript!";
let count: number = 42;
let isActive: boolean = true;

// Type inference - TypeScript figures out the type
let inferred = "I'm a string"; // TypeScript knows this is string

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

console.log(greet("Alice")); // Works
// console.log(greet(42));   // Error: Argument of type 'number' is not assignable

// Object type
interface User {
  id: number;
  name: string;
  email?: string; // optional property
}

const user: User = {
  id: 1,
  name: "Alice"
};

console.log(user.name);