Book Image

Learning TypeScript 2.x - Second Edition

By : Remo H. Jansen
Book Image

Learning TypeScript 2.x - Second Edition

By: Remo H. Jansen

Overview of this book

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.
Table of Contents (17 chapters)

Unit testing and test coverage

Unit testing refers to the practice of testing certain functions and areas (units) of our code. This gives us the ability to verify that our functions work as expected.

It is expected that the reader will have some understanding of the unit test process, but the contents exposed here will be covered at a much higher level of detail in Chapter 14, Application Testing.

At the beginning of this chapter, we included the most important parts of the application included in the companion source code for this chapter. The source code defined a calculator with support for two operations: pow and add.

The pow operation expects two numbers as its arguments and has two possible execution paths:

  • The pow function will throw an exception if one of the two arguments provided is not a number
  • The pow function will return a number if both arguments are valid numbers...