angular.service vs angular.factory

Question

I have seen both angular.factory() and angular.service() used to declare services; however, I cannot find angular.service anywhere in official documentation.

Answer 1

The factory pattern is more flexible as it can return functions and values as well as objects.

There isn't a lot of point in the service pattern IMHO, as everything it does you can just as easily do with a factory. The exceptions might be:

• If you care about the declared type of your instantiated service for some reason - if you use the service pattern, your constructor will be the type of the new service.
• If you already have a constructor function that you're using elsewhere that you also want to use as a service (although probably not much use if you want to inject anything into it!).

Arguably, the service pattern is a slightly nicer way to create a new object from a syntax point of view, but it's also more costly to instantiate. Others have indicated that angular uses "new" to create the service, but this isn't quite true - it isn't able to do that because every service constructor has a different number of parameters. What angular actually does is use the factory pattern internally to wrap your constructor function. Then it does some clever jiggery pokery to simulate javascript's "new" operator, invoking your constructor with a variable number of injectable arguments - but you can leave out this step if you just use the factory pattern directly, thus very slightly increasing the efficiency of your code.