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Learning TypeScript 2.x
Learning TypeScript 2.x

Learning TypeScript 2.x: Develop and maintain captivating web applications with ease , Second Edition

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Learning TypeScript 2.x

Working with Types

In the preceding chapter, we learned some basic concepts about the TypeScript type system, including the basics about the type inference system and the optional static type annotations.

In this chapter, you will learn about the main features of the TypeScript type system, including the following concepts:

  • The line between TypeScript and JavaScript
  • The features of the type system
  • Union types, intersection types, and discriminated unions
  • Type aliases and local types
  • The typeof and keyof operators
  • Control flow analysis and type guards
  • Non-nullable types
  • Generic types
  • Mapped types, lookup types, and conditional types

The TypeScript type system's characteristics

In this section, we are going to learn about the main characteristics of the TypeScript type system, including concepts such as type inference, optional type annotation, and the differences between a nominal type system and a structural type system.

The line between TypeScript and JavaScript

One of the most important things that you are going to need to master to become a good TypeScript programmer is to be able to understand where TypeScript ends and JavaScript begins. It is very important to be able to understand what happens with our TypeScript code at three important phases:

  • Design time: This takes place when we are writing our TypeScript code and designing our application...

Core features of the TypeScript type system

In this section, we are going to learn about some of the core features of the TypeScript type system. This includes concepts such as union types, intersection guards, type guards, and type aliases.

Union types

TypeScript allows you to declare union types:

let path: string[]|string;
path = "/temp/log.xml";
path = ["/temp/log.xml", "/temp/errors.xml"];
path = 1; // Error

In the preceding example, we have declared a variable named path that can contain a single path (string) or a collection of paths (array of strings). In the example, we have also set the value of the variable. We assigned a string and an array of strings without errors; however, when we attempted...

Literal types

Literal types allow us to declare the exact value that a string Boolean or number must have. When we declare a variable using the let keyword, its value will be inferred as a primitive type:

let five = 5; // number
let falsy = false; // boolean
let shape = "rectangle"; // string

However, if we use the const keyword, the type is inferred as the actual assigned value:

const five = 5; // 5
const falsy = false; // false
const shape = "rectangle"; // rectangle

Literal types can be used in combination with union types, type guards, and type aliases with ease:

type ShapeKind = "square" | "rectangle" | "circle";

Literal types can be used in combination with type guards and the power of control flow analysis to narrow union types using a technique known as discriminated unions.

...

Advanced features of the TypeScript type system

In this section, we are going to learn some advanced type system features such as generic types, mapped types, and lookup types.

Generic types

Generic types can help us avoid using type casting and increase the reusability of our code by allowing us to declare (T) when a function, class, or method is consumed, as opposed to when it is declared:

function deserialize<T>(json: string): T {
return JSON.parse(json) as T;
}

interface User {
name: string;
age: number;
}

let user = deserialize<User>(`{"name":"Remo","age":28}`);

interface Rectangle {
width: number;
height: number;
}

let rectangle = deserialize<Rectangle>(`{&quot...

Summary

In this chapter, we learned about many of the features of the TypeScript type system. At this point, we should now have a good understanding of concepts such type inference, non-nullable types, structural typing, and control flow analysis.

In the next chapter, we will learn more about the usage of functions in TypeScript.

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Key benefits

  • Develop modular, scalable, maintainable, and adaptable web applications by taking advantage of TypeScript
  • Walk through the fundamentals of TypeScript with the help of practical examples
  • Enhance your web development skills using TypeScript 2.x

Description

TypeScript is an open source and cross-platform statically typed superset of JavaScript that compiles to plain JavaScript and runs in any browser or host. This book is a step-by-step guide that will take you through the use and benefits of TypeScript with the help of practical examples. You will start off by understanding the basics as well as the new features of TypeScript 2.x. Then, you will learn how to work with functions and asynchronous programming APIs. You will continue by learning how to resolve runtime issues and how to implement TypeScript applications using the Object-oriented programming (OOP) and functional programming (FP) paradigms. Later, you will automate your development workflow with the help of tools such as Webpack. Towards the end of this book, you will delve into some real-world scenarios by implementing some full-stack TypeScript applications with Node.js, React and Angular as well as how to optimize and test them. Finally, you will be introduced to the internal APIs of the TypeScript compiler, and you will learn how to create custom code analysis tools.

Who is this book for?

If you are a developer aiming to learn TypeScript to build attractive web applications, this book is for you. No prior knowledge of TypeScript is required. However, a basic understanding of JavaScript would be an added advantage.

What you will learn

  • Understand TypeScript in depth, including its runtime and advanced type system features
  • Master the core principles of the object-oriented programming and functional programming paradigms with TypeScript
  • Save time using automation tools such as Gulp, Webpack, ts-node, and npm scripts
  • Develop robust, modular, scalable, maintainable, and adaptable applications with testing frameworks such as Mocha, Chai, and Sinon.JS
  • Put your TypeScript skills to practice by developing full-stack web applications with Node.js, React and Angular
  • Use the APIs of the TypeScript compiler to build custom code analysis tool
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Publication date : Apr 30, 2018
Length: 536 pages
Edition : 2nd
Language : English
ISBN-13 : 9781788391474
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Table of Contents

16 Chapters
Introducing TypeScript Chevron down icon Chevron up icon
Working with Types Chevron down icon Chevron up icon
Working with Functions Chevron down icon Chevron up icon
Object-Oriented Programming with TypeScript Chevron down icon Chevron up icon
Working with Dependencies Chevron down icon Chevron up icon
Understanding the Runtime Chevron down icon Chevron up icon
Functional Programming with TypeScript Chevron down icon Chevron up icon
Working with Decorators Chevron down icon Chevron up icon
Automating Your Development Workflow Chevron down icon Chevron up icon
Node.js Development with TypeScript Chevron down icon Chevron up icon
Frontend Development with React and TypeScript Chevron down icon Chevron up icon
Frontend Development with Angular and TypeScript Chevron down icon Chevron up icon
Application Performance Chevron down icon Chevron up icon
Application Testing Chevron down icon Chevron up icon
Working with the TypeScript Compiler and the Language Services Chevron down icon Chevron up icon
Other Books You May Enjoy Chevron down icon Chevron up icon

Customer reviews

Rating distribution
Full star icon Full star icon Empty star icon Empty star icon Empty star icon 2
(1 Ratings)
5 star 0%
4 star 0%
3 star 0%
2 star 100%
1 star 0%
Mr. T. Hamilton Jul 01, 2019
Full star icon Full star icon Empty star icon Empty star icon Empty star icon 2
I bought this book expecting a comprehensive look into Typescript, having very minimal experience with JavaScript. What I got was a book which felt to be hastily put together. The author has an idea of what he wants to talk about in each chapter, but instead of laying out a clear and coherent explanation of what he's trying to say, there's a rushed and scatter gun approach to explaining topics. The English quality is also not great, and the editing has allowed many typos to get in, which I think in itself speaks for the quality of this book.I would not recommend buying this book and instead looking at the official documentation, or reading one of the better JavaScript books then supplementing your knowledge with a brief overview of TypeScript elsewhere.
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