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TypeScript: Basic and Advanced Types

1. Primitive Types​

TypeScript allows you to explicitly declare all of JavaScript's basic data types.

let isDone: boolean = false;
let age: number = 30;
let userName: string = "Alice";
let list: number[] = [1, 2, 3]; // Array
let tuple: [string, number] = ["hello", 10]; // Tuple

2. Union and Intersection​

  • Union (|): Allows a value to be one of several types.
  • Intersection (&): Combines multiple types into one.
// Union
let code: string | number = 101;
code = "A101";

// Intersection
interface Person { name: string; }
interface Employee { id: number; }
type Staff = Person & Employee;

const newStaff: Staff = { name: "Bob", id: 123 };

3. Any, Unknown, and Never​

  • Any: Allows any type. (Best to avoid frequent use)
  • Unknown: Allows any type but requires type checking before use, making it safer than any.
  • Never: Represents the type of values that reflect something that will never occur (e.g., a function that always throws an error).

4. Enum (Enumerated Type)​

Enums allow you to define a set of named constants, either as numbers or strings.

enum Direction {
  Up = 1,
  Down,
  Left,
  Right,
}
let move: Direction = Direction.Up;
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