TypeScript TypeScript Type System & Generics 2

Question 1

What is a union type in TypeScript?

Accepted Answer

A type that can be one of several specified types

Answer

A union type (written as `A | B`) allows a variable to hold a value of type A or type B, enabling flexible yet type-safe code.

Question 2

What is an intersection type in TypeScript?

Accepted Answer

A type that combines multiple types into one, requiring all properties

Answer

An intersection type (written as `A & B`) combines multiple types so the resulting type has all properties of A and all properties of B.

Question 3

Which utility type constructs a type by picking a set of properties from another type?

Accepted Answer

Pick<T, K>

Answer

`Pick<T, K>` creates a new type by selecting only the specified keys K from type T, effectively narrowing the shape.

Question 4

What does `Readonly<T>` do in TypeScript?

Accepted Answer

Makes all properties of T immutable after assignment

Answer

`Readonly<T>` constructs a type with all properties of T marked as `readonly`, preventing reassignment after object creation.

Question 5

In TypeScript, what is a literal type?

Accepted Answer

A type inferred from a literal value like `42` or `'hello'`

Answer

Literal types restrict a variable to one specific value, such as `type Direction = 'left' | 'right'`, providing extremely precise type constraints.

TypeScript Practice Test