TypeScript: Conditional Types Explained

TypeScript: Conditional Types Explained

TypeScript: Conditional Types Explained. Learn what conditionals are and how they are used in TypeScript. Also introduced in the TypeScript handbook, allow us to deterministically define types depending on what parameterised types consist of.

Conditionals in TypeScript, also introduced in the  TypeScript handbook, allow us to deterministically define types depending on what parameterised types consist of. The general basic rule is:

type ConditionalType = T extends U ? X : Y

If parameter _T_ extends some type _U_ , then assign _X_ , otherwise assign _Y_.

The extends keyword is at the heart of conditionals whereby we are checking if every value of T can be assigned to a value of U. If T is assignable to U, then the “true type” will be returned — X is our case. If T is not assignable to U, then the false type, Y, will be returned.

As a basic example, consider checking whether some type extends a primitive such as a string, and assign never if it does not:

type StringOrNot = SomeType extends string ? string : never;

The _never_ keyword indicates that a value will never occur — we will cover _never_ in more detail further down when conditionals are used to coincide with type filtering.

development typescript javascript

Bootstrap 5 Complete Course with Examples

Bootstrap 5 Tutorial - Bootstrap 5 Crash Course for Beginners

Nest.JS Tutorial for Beginners

Hello Vue 3: A First Look at Vue 3 and the Composition API

Building a simple Applications with Vue 3

Deno Crash Course: Explore Deno and Create a full REST API with Deno

How to Build a Real-time Chat App with Deno and WebSockets

Convert HTML to Markdown Online

HTML entity encoder decoder Online

Hire Dedicated JavaScript Developers -Hire JavaScript Developers

Hire dedicated JavaScript Developers who are proficient in AngularJS, ReactJS, NodeJS, & VueJS frameworks. Get flexible hiring models as per your business requirements.

TypeScript Tutorial For JavaScript Developers - TypeScript Basics

TypeScript Tutorial For JavaScript Developers - TypeScript Basics. I will show you guys 4 example of JavaScript code, and how to convert it to TypeScript. This is a typescript beginners tutorial.

What, Why, and How of Typescript for JavaScript Developers

What, Why, and How of Typescript for JavaScript Developers. If you are a Javascript developer, you must have heard about Typescript at one point or another. What is Typescript, what is its type system, and how would it benefit you as a Javascript developer to use Typescript in your next project?

What is TypeScript? Why TypeScript? and Why Not TypeScript?

TypeScript extends JavaScript by adding Types. There are many great reasons to switch to TypeScript. Especially if your team uses JavaScript. There are some reasons to not use TypeScript as there are with any language or framework.

How long does it take to develop/build an app?

This article covers A-Z about the mobile and web app development process and answers your question on how long does it take to develop/build an app.