Typed Functions

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

// Arrow function with types
const greetArrow = (name: string): string => `Hello, ${name}!`;

// Optional parameters
function createUser(name: string, age?: number): User {
  return {
    id: Math.random(),
    name,
    createdAt: new Date(),
    ...(age && { age })
  };
}

// Default parameters
function multiply(a: number, b: number = 2): number {
  return a * b;
}

// Rest parameters
function sum(...numbers: number[]): number {
  return numbers.reduce((a, b) => a + b, 0);
}

// Function overloads
function format(value: string): string;
function format(value: number): string;
function format(value: string | number): string {
  if (typeof value === "string") {
    return value.toUpperCase();
  }
  return value.toFixed(2);
}

// Generic functions
function identity<T>(value: T): T {
  return value;
}

function mapArray<T, U>(arr: T[], mapper: (item: T) => U): U[] {
  return arr.map(mapper);
}

// Usage
const result1 = identity<string>("hello");
const result2 = identity(42);

const numbers = [1, 2, 3];
const strings = mapArray(numbers, n => n.toString());