Book Image

Mastering TypeScript - Fourth Edition

By : Nathan Rozentals
Book Image

Mastering TypeScript - Fourth Edition

By: Nathan Rozentals

Overview of this book

TypeScript is both a language and a set of tools to generate JavaScript, designed by Anders Hejlsberg at Microsoft to help developers write enterprise-scale JavaScript. Mastering Typescript is a golden standard for budding and experienced developers. With a structured approach that will get you up and running with Typescript quickly, this book will introduce core concepts, then build on them to help you understand (and apply) the more advanced language features. You’ll learn by doing while acquiring the best programming practices along the way. This fourth edition also covers a variety of modern JavaScript and TypeScript frameworks, comparing their strengths and weaknesses. You'll explore Angular, React, Vue, RxJs, Express, NodeJS, and others. You'll get up to speed with unit and integration testing, data transformation, serverless technologies, and asynchronous programming. Next, you’ll learn how to integrate with existing JavaScript libraries, control your compiler options, and use decorators and generics. By the end of the book, you will have built a comprehensive set of web applications, having integrated them into a single cohesive website using micro front-end techniques. This book is about learning the language, understanding when to apply its features, and selecting the framework that fits your real-world project perfectly.
Table of Contents (19 chapters)
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Observable errors

So what happens when something goes wrong within an Observable stream? Obviously, we will need a mechanism to catch these errors, so that we can do something sensible with them. As an example of a faulty Observable stream, consider the following code:

interface IValue {
    value: number
interface INestedObj {
    id?: IValue;
const objEmit : Observable<INestedObj> = of(
    { id: { value: 1 } },
    { id: { value: 2 } }

Here, we start with two interfaces, named IValue and INestedObj. The IValue interface has a property named value of type number, and the INestedObj has a single optional parameter named id of type IValue. We then create an Observable named objEmit that emits three values. The first value has the nested structure described by the INestedObj interface, and the second is a blank object. Now consider the following Observable stream:

const returnIdValue = objEmit.pipe(
    map((value: INestedObj) => {