Type Choices in JavaScript/TypeScript

Use these notes to explain when to use types, interfaces, and classes in TS.

Type vs interface

• Type aliases: Great for unions, primitives, and utility types.
• Interfaces: Good for object shapes and extension via declaration merging.

type Status = 'idle' | 'loading' | 'error';

interface User {
  id: string;
  name: string;
}

Classes

• Use for stateful logic or when you need instanceof checks.
• Keep constructors simple; move side effects elsewhere.

Generics

• Apply generics to make utilities reusable.

const identity = <T>(value: T): T => value;

Interview prompt

• When do you prefer type over interface and why?