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
TypeScript Tools and Framework Options

The State pattern

The GoF describe two design patterns named the State pattern, and the Mediator pattern. The State pattern uses a set of concrete classes that are derived from a base class to describe a particular state. As an example, consider creating an enum to describe the states that a door can be in. At first glance, a door could be either Open or Closed. In this case, a simple if...else control flow will likely take care of any logic we wish to apply.

Consider, however, what happens to our control flow and logic if we needed a Locked and Unlocked state, or if it were a sliding door for a SlightlyAjar, HalfOpen, AlmostFullyOpen, and FullyOpen state. The State design pattern allows us to easily define these states, and adjust our logic based on the current state of an object.

If we think about our application a little, we know that our screens will be in one or another particular...