Javascript

Promises are a great solution to address complexities of asynchronous requests and responses. AngularJS provides Promises using services such as $q and $http; other services also use promises, but I will not discuss those here.

Promises allow developers to easily attach 1x-only notifications of response to any asynchronous request/action. Promises also enable two (2) other very important things. We can:

• Transform the responses before subsequent handlers (in the chain) are notified of the response.
• Use the response to invoke more async requests (which could generate more promises).

But even more important than the features above, Promises support easy chaining of custom activity or computations. Managing sequences or chains of asynchronous activity can be a very difficult and complex effort. Promise chains are amazing and provide means to easily build sequences of asynchronous requests or asynchronous activity.