How to check in AngularJS if a service was register or not

There are cases when you need to check in a service or a controller was register in AngularJS.
For example a valid use case is when you have the same implementation running on multiple application. In this case, you may want to intercept the HTTP provider and add a custom step there. This step don’t needs to run on all the application, only in the one where the service exist and register.
A solution for this case would be to have a flag in the configuration that specify this. In the core you would have an IF that would check the value of this flag.
Another solution is to check if a specific service was register in AngularJS or not. If the service was register that you would execute your own logic.
To check if a service was register or not in AngularJS container you need to call the ‘has’ method of ‘inhector’. It will return TRUE if the service was register.

if ($injector.has('httpInterceptorService')) {
            $httpProvider.interceptors.push('httpInterceptorService');
}

The downside of this solution is that you will have the code in all the application, even in the application that don’t need that logic.
This problem can be resolved very easily if you extract the custom logic to a separate JS that can/would exist only where is needed.