Type alias for objects in Typescript - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a type alias in TypeScript?

A type alias is a name given to a specific type, including object shapes, so you can reuse it easily in your code.

beginner

How do you define a type alias for an object with properties name (string) and age (number)?

You write:

type Person = { name: string; age: number; };

intermediate

Can a type alias describe optional properties in an object? How?

Yes, by adding a question mark after the property name. Example:

type Person = { name: string; age?: number; };

Here, age is optional.

beginner

What happens if you try to assign an object missing a required property to a variable typed with a type alias?

TypeScript will show an error because the object does not match the required shape defined by the type alias.

intermediate

Can type aliases be used to describe nested objects? Give an example.

Yes. Example:

type Address = { city: string; zip: string; };
type Person = { name: string; address: Address; };

How do you create a type alias for an object with a string property 'title' and a number property 'pages'?

A interface Book = { title: string; pages: number; };

B type Book = (title: string, pages: number);

C type Book = { title: string; pages: number; };

D let Book = { title: string; pages: number; };

Option C correctly defines a type alias for an object with the specified properties.

Which symbol marks a property as optional in a TypeScript type alias?

A ?

B !

C *

D #

The question mark (?) after a property name makes it optional.

What will TypeScript do if you assign an object missing a required property to a variable typed with a type alias?

A Convert the object to any type

B Ignore the missing property

C Automatically add the missing property

D Show an error

TypeScript enforces the shape defined by the type alias and will show an error if required properties are missing.

Can type aliases be used to describe nested objects?

A Yes

B No

C Only with interfaces

D Only with classes

Type aliases can describe nested objects by referencing other type aliases.

Which keyword is used to create a type alias in TypeScript?

A interface

B type

C alias

D class

The 'type' keyword is used to create type aliases.

Explain how to create a type alias for an object with both required and optional properties.

Think about how to mark properties optional in the object.

Describe how nested objects can be represented using type aliases in TypeScript.

Consider defining one type alias inside another.