Types in TypeScript

In TypeScript, types are a way to describe the shape of a value, telling us what kind of data it holds. This helps catch errors during development, making your code more robust and easier to maintain. TypeScript offers a rich set of built-in types, and you can also create your own.

Primitive Types
Object Types
Special Types
Union and Intersection Types
Type Inference

Primitive Types

These are the most basic types of data.

string

let message: string = "Hello, TypeScript!";

number

let age: number = 30;
let price: number = 19.99;

boolean

let isDone: boolean = false;

null

let currentName: string | null = null;

undefined

let undeclaredVariable: undefined;

symbol

const id = Symbol('user_id');
let userId: symbol = id;

bigint

let veryLargeNumber: bigint = 123456789012345678901234567890n;

Object Types

These represent more complex data structures.

any

let dynamicValue: any = 42;
dynamicValue = "Now I'm a string!";

object

let userObject: object = { name: "Alice", age: 25 };

Special Types

void

function logMessage(message: string): void {
  console.log(message);
}

never

function throwError(message: string): never {
  throw new Error(message);
}

Union and Intersection Types

Union Types (|)

let status: "pending" | "success" | "error" = "pending";
status = "success";

Intersection Types (&)

interface Draggable {
  drag(): void;
}
interface Resizable {
  resize(): void;
}

type UIWidget = Draggable & Resizable;

let textBox: UIWidget = {
  drag: () => { },
  resize: () => { }
};

Type Inference

TypeScript has a powerful feature called type inference. If you do not explicitly provide a type annotation, TypeScript will try to infer the type based on the value assigned.

let greeting = "Hello";

Understanding these types is fundamental to writing effective TypeScript code. You can combine them to create complex and type-safe applications.

Isaac.