Angular applications can be coded in a wide variety of languages and syntaxes: ECMAScript 5, Dart, ECMAScript 6, TypeScript, or ECMAScript 7.

TypeScript is a typed superset of ECMAScript 6 (also known as ECMAScript 2015) that compiles to plain JavaScript and is widely supported by modern OSes. It features a sound object-oriented design and supports annotations, decorators, and type checking.

The reason why we picked (and obviously recommend) TypeScript as the syntax of choice for instructing how to develop Angular applications in this book is based on the fact that Angular itself is written in this language. Being proficient in TypeScript will give the developer an enormous advantage when it comes to understanding the guts of the framework.

On the other hand, it is worth remarking that TypeScript's support for annotations and type introspection turns out to be paramount when it comes to managing dependency injection and type binding between components with a minimum code footprint, as we will see further down the line in this book.

Ultimately, you can carry out your Angular projects in plain ECMAScript 6 syntax if that is your preference. Even the examples provided in this book can be easily ported to ES6 by removing type annotations and interfaces, or replacing the way dependency injection is handled in TypeScript with the most verbose ES6 way.

For the sake of brevity, we will only cover examples written in TypeScript and actually recommend its use because of its higher expressivity thanks to type annotations, and its neat way of approaching dependency injection based on type introspection out of such type annotations.