In TypeScript, Aliases and Interfaces are tools for defining the shape of data. Both serve similar purposes but have distinct use cases and capabilities. Here's an in-depth look at both:

1. Type Aliases

A Type Alias is a way to give a type a custom name. It can represent primitives, unions, tuples, or more complex structures.

Syntax:

typescript
// Primitive aliastype ID = string | number;// Object aliastype User = {  id: ID;  name: string;  isAdmin?: boolean; // Optional property};// Using aliasesconst user: User = { id: 1, name: "John Doe" };

Key Features of Type Aliases:

• Can define unions and tuples:

  typescript
  type Response = "success" | "error";type Coordinates = [number, number];
  

• Can define function types:

  typescript
  type Add = (a: number, b: number) => number;
  

2. Interfaces

An Interface is used to define the structure of an object or class. It is more focused on defining objects and contracts.

Syntax:

typescript
interface InterfaceName {  property: Type;  method(param: Type): ReturnType;}

Example:

typescript
interface User {  id: number;  name: string;  isAdmin?: boolean; // Optional property}// Using interfacesconst admin: User = { id: 1, name: "Admin", isAdmin: true };

Key Features of Interfaces:

• Inheritance: Interfaces can extend other interfaces.

  typescript
  interface Person {  name: string;}interface Employee extends Person {  employeeId: number;}
  

• Merging: Interfaces with the same name automatically merge.

  typescript
  interface Settings {  theme: string;}interface Settings {  layout: string;}// Merged:const config: Settings = { theme: "dark", layout: "grid" };
  

Comparison: Type Aliases vs. Interfaces

Best Practices

• Use interfaces when defining the structure of objects or working with classes.
• Use type aliases when dealing with more complex types like unions, tuples, or function types.