Creating type aliases in Typescript - Quick Revision & Summary

Recall & Review

beginner

What is a type alias in TypeScript?

A type alias is a way to give a new name to a type. It helps make code easier to read and reuse by creating a simple name for complex types.

beginner

How do you create a type alias for a string in TypeScript?

You use the type keyword followed by the new name and the type. For example:

type Name = string;

intermediate

Can type aliases represent union types? Give an example.

Yes, type aliases can represent union types. For example:

type Status = "success" | "error" | "loading";

This means Status can be one of those three string values.

intermediate

What is the difference between a type alias and an interface in TypeScript?

Type aliases can name any type, including primitives, unions, and tuples. Interfaces describe object shapes and can be extended. Type aliases cannot be reopened to add new properties, but interfaces can.

beginner

Show how to create a type alias for an object with properties id (number) and name (string).

You write:

type User = { id: number; name: string; };

This creates a new type called User representing that object shape.

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

A type

B alias

C interface

D class

The type keyword is used to create type aliases.

What does this type alias represent?

type ID = number | string;

A ID can only be a number

B ID is a function

C ID can be a number or a string

D ID is an object

The union number | string means ID can be either a number or a string.

Can a type alias be used to name a tuple type?

A Only with classes

B Yes

C Only with interfaces

D No

Type aliases can name tuple types, for example: type Point = [number, number];

Which of these can type aliases NOT do?

A Name object types

B Represent union types

C Name primitive types

D Extend other types by reopening

Type aliases cannot be reopened to add new properties or extend like interfaces can.

What is the correct syntax to create a type alias for an object with a string property 'title'?

A type Book = { title: string; };

B interface Book = { title: string; };

C class Book { title: string; }

D alias Book = { title: string; };

The correct syntax uses type followed by the name and the object shape.

Explain what a type alias is and how it helps in TypeScript programming.

Think about giving a nickname to a type.

Describe the difference between a type alias and an interface in TypeScript.

Focus on their capabilities and usage.