In order to ease the transition from AngularJS 1.x apps to Angular 2, the http module should be possible to be used in AngularJS 1.x applications, though not necessarily as a drop-in replacement for $http.

Some considerations:

• DI and module systems are different, but the current architecture should allow for easily creating a module and service for http. refactor(http): move http into its own module as sibling of angular2 #2680 will make this easier.
• There is currently no notion of global interceptors or transformers, though these could be encapsulated in an AngularJS 1.x service/provider.
• The new library is based on observables instead of promises. The observable should be easily converted to a promise as a convenience, but the encouraged path should be to use the observable.
• Http doesn't hook into AngularJS 1.x's digest loop.
• The test lib would also need to be bundled separately and made to work with 1.x.
• Where should 1.x-friendly documentation live?