TypeScript

// Basic types
let name: string = "John"
let age: number = 30
let isActive: boolean = true
let value: any = "anything"

// Arrays
let numbers: number[] = [1, 2, 3]
let names: Array<string> = ["Alice", "Bob"]

// Tuple
let tuple: [string, number] = ["hello", 10]

// Enum
enum Color { Red, Green, Blue }
let color: Color = Color.Green

// Type alias
type ID = string | number;

// Union (one of)
type Status = "active" | "inactive" | "pending";

// Intersection (combine all)
type Employee = Person & { company: string };

// Literal types
type Direction = "up" | "down" | "left" | "right";

interface User {
  id: number;
  name: string;
  email?: string;        // Optional
  readonly createdAt: Date; // Cannot be changed
}

// Extending interfaces
interface Admin extends User {
  permissions: string[];
}

// Index signatures
interface Dictionary {
  [key: string]: string;
}

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

// Generic interface
interface Box<T> {
  value: T;
}

// Constraints
function getLength<T extends { length: number }>(item: T): number {
  return item.length;
}

// Multiple type params
function pair<K, V>(key: K, value: V): [K, V] {
  return [key, value];
}

// Partial - all properties optional
type PartialUser = Partial<User>;

// Required - all properties required
type RequiredUser = Required<User>;

// Pick - select specific properties
type UserName = Pick<User, "name" | "email">;

// Omit - exclude properties
type UserWithoutId = Omit<User, "id">;

// Record - key-value mapping
type Roles = Record<string, string[]>;

// ReturnType
type Fn = () => string;
type Result = ReturnType<Fn>; // string