In angular2 they are for example used for dependency injection, which works really well. Other use cases that I see are for example automatically generating [d

In angular2 they are for example used for dependency injection, which works really well. Other use cases that I see are for example automatically generating [de]serialization code for members based on decorators and their values (like how Annotations are used in C# and Java serialization frameworks or tags in Go). There are also web frameworks popping up which use decorators for routing and parameter binding in a similar fashion how some Java frameworks work.