As services are reusable singleton objects in AngularJS which is used to organize and share codes across the application, they can be injected into filters, controllers, and directives. Angular 2 offers three ways to create a service; factory, service, and provider.

The factory function allows developers to include some logic before creating the object and returns the created object. The syntax for factory function is as follows.

app.factory('serviceName',function(){ return serviceObj;})

BY Best Interview Question ON 24 Jun 2020