This book is for developers who know JavaScript but have never touched Typescript.

Chapter 1, Getting Started with TypeScript, covers how to bring TypeScript into a new project or an existing JavaScript project. We will see how to set up your environment in your current build setup. TypeScript is supported by a variety of build tools, such as Grunt, Gulp, Webpack, or simply using the CLI. We also dive into the essential options, among all the ones that are available, to help you get started with TypeScript.

Chapter 2, Onboarding Types with Primitive, illustrates scoping a variable, the subtlety between undefined variables and null variables, and how to make a variable optional or required. At the end of this chapter, the reader will be in a situation where all the variables will be declared properly with an type that's accurate supported by TypeScript. The distinction between a primitive and non-primitive type will not be a conundrum anymore. The use of enum or symbol will be natural, and the creation of new types will become a habit any time a new domain object is introduced in your system.

Chapter 3, Unleashing the Power of Type with Objects, illustrates the difference between an object, Object, object literal and an object built with a constructor. This chapter also introduces the notion of a union between types that will allow an infinite combination of types for a single value. Furthermore, the concept of intersection is introduced, which allows us to manipulate type differently. At the end of this chapter, the reader will be able to create complex combinations of objects that hold advanced structures. We will dissect how to create a dictionary with a strongly typed index signature, understand how type can be beneficial with a map, and how to use the right object in order to be as accurate as possible when defining an object that can have a broad reach.

Chapter 4, Transforming Your Code in Object-Oriented, explains that object-oriented programming has its own set of terminology, and TypeScript relies on many of them. In this chapter, all the concepts of object-oriented programming that TypeScript supports are discussed with examples. We will see what a class is and how to instantiate a class into an object. In the same vein, we will see how a constructor can be strongly typed with TypeScript, but also how with a shorthand syntax we can assign a class's fields directly from the constructor. The principle of encapsulation with visibility, how to implement an interface, and how to bring abstraction to a class are all covered.

Chapter 5, Scoping Variables with Different Patterns,covers the subtlety the most basic concept, which is the variable. Knowing the exact type from a primitive to an object is essential for accessing specific members. Scoping down the exact type at runtime and design time is crucial for consistency between the two environments and to have feedback about what is possible or not. The variety of configuration among the different types of variable requires many different patterns that are covered in this chapter.

Chapter 6, Reusing Code through Generic, builds on ideas introduced in the previous chapters. The chapter builds these ideas by enhancing type and making them generic. Basic topics, such as defining a generic class and interface, are present. Through the chapter, we move into more advanced topics, such as generic constraints. The goal of this chapter is to make your code more generic to increase the reusability of your classes, functions, and structures to reduce the burden of duplicating code.

Chapter 7, Mastering the Art of Defining Types,covers how to create type from libraries that we are not working directly with but by importing the library inside your TypeScript project. The main difference is that when consuming code outside your project, you will not directly use TypeScript code but their definition. The reason is that JavaScript is provided in those libraries, not TypeScript code. We will see how it is possible to master the art of creating definition files for code that does not provide them, allowing you to keep working in a strong environment.

This book is for JavaScript developers who want to get started with TypeScript for building applications. No previous knowledge of TypeScript is expected.

let a:number = 2;
a = "two"; // Doesn't compile

function switchFunction(num: number) {
let b: string = "functionb";

   switch (num) {
       case 1:
   let b: string = "case 1";
       break;
   }
}

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