JavaScript TypeScript Basics 2

Question 1

What does the `readonly` modifier do to a property in TypeScript?

Accepted Answer

Prevents the property from being reassigned after initialization

Answer

The `readonly` modifier prevents a property from being reassigned after it is set during initialization or in the constructor.

Question 2

Which TypeScript utility type makes all properties of a type optional?

Accepted Answer

Partial<T>

Answer

`Partial<T>` constructs a type with all properties of T set to optional.

Question 3

What is a TypeScript `enum` used for?

Accepted Answer

Defining a set of named numeric or string constants

Answer

Enums allow you to define a set of named constants, making intent clearer and reducing magic values.

Question 4

What does the `keyof` operator return in TypeScript?

Accepted Answer

A union type of all property names of a given type

Answer

`keyof T` produces a union type of all the keys (property names) of type T.

Question 5

How do you declare a variable that can be either a `string` or `null` in TypeScript?

Accepted Answer

let x: string | null;

Answer

The union type `string | null` correctly allows a variable to hold either a string or null.

JavaScript Practice Test