Book Image

Mastering TypeScript - Fourth Edition

By : Nathan Rozentals
4.7 (3)
Book Image

Mastering TypeScript - Fourth Edition

4.7 (3)
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)
17
Other Books You May Enjoy
18
Index

Observables returning Observables

Quite often, when working with Observables, we need to return a new Observable stream while already dealing with an Observable stream. In other words, for each Observable value in a stream, create a new Observable stream. While this might sound complicated, in the real world, it can happen fairly regularly.

Suppose that we are working with a REST API that tells us what products are sold within a sales catalog. This particular API call returns an array of product IDs that are associated with a particular catalog. For each of these product IDs, we then need to initiate a new REST API call to retrieve the information for this particular product, such as its name and description.

Let's assume that we are using an HTTP client that returns an Observable for each API call. This means that the first Observable stream will be the list of products within a catalogue, say, [1,2,3]. For each value in this stream, we then need to initiate a new API...