Well angular 4 supports ES6. So, you can you arrow functions without any second thought. But, wait there is a catch. Angular 4 recommends use of typescript ( You can code in plain ES6 though ) .

Typescript is basically a type system which forces you to define datatype for variables, objects before consuming them so that type errors can be identified at compile time itself instead of run-time.

Pros & Cons :

• Awesome framework ( A complete framework ) with native support of ( Routing , Forms & Validations , Client & Server rendering , Animations etc ) unlike React where you need to select third party libraries to complete frontend.
• Default typescript. ( React also supports typescript , flow and proptypes based type checking but not by default ). In starting typescript bugs you a lot but, over time you will enjoy using it.
• Not smart as React while handling Dom manipulations. React clearly wins by using Virtual DOM .
• Modular coding style similar to React. ( Recommends creating highly reusable components.)
• Little confusing at first and requires time before you become comfortable with Angular.