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Aliases and Interfaces in TypeScript

Overview

TypeScript provides two primary ways to define custom types: type aliases and interfaces. Both are used to describe the shape of an object or other types, but they have distinct features and use cases.

Type Aliases

A type alias is a way to give a type a name. It can represent strings,objects, arrays, and more.

Syntax

type AliasName = TypeDefinition;

Example

type StringAlias = string;
type Point = { x: number; y: number };
type UnionType = string | number;

Features

  1. Can represent any type, including primitives, unions, intersections, and tuples.
  2. Cannot be reopened or extended after creation.

Interfaces

An interface is like aliases, but only apply to object types.

Syntax

interface InterfaceName {
  property: Type;
}

Example

interface Point {
  x: number;
  y: number;
}

interface Drawable extends Point {
  draw(): void;
}

Features

  1. Can only describe object shapes.
  2. Supports extension through inheritance (extends keyword).
  3. Can be reopened and augmented across different declarations.