TypeScript

You can use either of TypeScript, JavaScript, or Dart to build an Angular 2 app. In this tutorial we will choose TypeScript.

TypeScript has benefits such as intellisense and code completion.

For example, when the function needs a string but get a number, the IDE will show the error:

It can also speed up your development. When you want to input _.map, and you just typed _.m, it already shows the map:

TypeScript is a typed superset of JavaScript that compiles to plain JavaScript. Basically,

TypeScript = Type + ES6 + part of ES7

Learn more

If you want to have deep understanding of TypeScript 2, TypeScript Deep Dive is a good resource.