Book Image

Mastering TypeScript 3 - Third Edition

By : Nathan Rozentals
Book Image

Mastering TypeScript 3 - Third Edition

By: Nathan Rozentals

Overview of this book

TypeScript is both a language and a set of tools to generate JavaScript. It was designed by Anders Hejlsberg at Microsoft to help developers write enterprise-scale JavaScript. Starting with an introduction to the TypeScript language, before moving on to basic concepts, each section builds on previous knowledge in an incremental and easy-to-understand way. Advanced and powerful language features are all covered, including asynchronous programming techniques, decorators, and generics. This book explores many modern JavaScript and TypeScript frameworks side by side in order for the reader to learn their respective strengths and weaknesses. It will also thoroughly explore unit and integration testing for each framework. Best-of-breed applications utilize well-known design patterns in order to be scalable, maintainable, and testable. This book explores some of these object-oriented techniques and patterns, and shows real-world implementations. By the end of the book, you will have built a comprehensive, end-to-end web application to show how TypeScript language features, design patterns, and industry best practices can be brought together in a real-world scenario.
Table of Contents (16 chapters)
Free Chapter
1
TypeScript Tools and Framework Options

Functions

So far, we have explored how to add type annotations to variables and objects. However, this simple syntax can also be used with functions in order to introduce type safety whenever a function is used. Let's now examine the type annotation syntax as it applies to functions, and explore these rules in more detail.

Function return types

Using the very simple syntactic sugar that TypeScript uses, we can easily define the type of a variable that a function should return. In other words, when we call a function, and it returns a value, what type should the return value be treated as?

Consider the following TypeScript code:

function addNumbers(a: number, b: number) : string { 
    return a + b; 
} 
var addResult...