TypeScript TypeScript Classes & Interfaces

Question 1

In TypeScript, what is the key difference between an `interface` and a `type` alias?

Accepted Answer

Interfaces support declaration merging; type aliases do not

Answer

Interfaces support declaration merging (multiple declarations of the same interface are merged), while type aliases cannot be reopened or merged after definition.

Question 2

Which access modifier restricts a class member to be accessible only within the class itself?

Accepted Answer

private

Answer

The `private` modifier limits access to a class member so it can only be used within the declaring class, not from subclasses or external code.

Question 3

What does the `implements` keyword do in a TypeScript class declaration?

Accepted Answer

Declares that the class satisfies the contract of an interface

Answer

The `implements` keyword tells TypeScript that a class must provide all properties and methods defined by the specified interface, acting as a contract check.

Question 4

What is an abstract class in TypeScript?

Accepted Answer

A class that cannot be instantiated directly and may contain abstract methods

Answer

An abstract class serves as a base class blueprint; it cannot be instantiated with `new` directly and may declare abstract methods that subclasses must implement.

Question 5

In TypeScript, what does parameter shorthand in a constructor do?

Accepted Answer

Declares and assigns class properties directly from constructor parameters using access modifiers

Answer

Adding an access modifier (like `public` or `private`) to a constructor parameter automatically creates and initializes a class property with the same name.

TypeScript Practice Test

TypeScript Practice Test

TypeScript TypeScript Classes & Interfaces