Classes & Interfaces

Preview — 3 of 10 questions

What is the purpose of an interface in TypeScript?

javascript

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

AIt creates a JavaScript class at runtime

BIt creates a singleton object

CIt defines the shape (contract) of an object — compile-time only, no runtime artifact

DIt is identical to type in every way

What does the ? modifier mean on an interface property?

javascript

interface Config {
  host: string;
  port?: number;
  debug?: boolean;
}

Aport must be provided but can be undefined

Bport defaults to 0 if not provided

Cport is read-only

Dport is optional — it can be omitted entirely or provided as number | undefined

What does implements guarantee?

javascript

interface Serializable {
  serialize(): string;
  deserialize(data: string): void;
}

class UserSession implements Serializable {
  serialize(): string { return JSON.stringify(this); }
  deserialize(data: string): void { Object.assign(this, JSON.parse(data)); }
}

AUserSession inherits the method implementations from Serializable

BUserSession can only be used where Serializable is expected

CTypeScript verifies at compile time that UserSession provides all methods declared in Serializable

Dimplements creates a prototype chain between the interface and the class

Answer all 10 questions (7 more), see explanations for every answer, and track your score.