AngularJS actually provides a way to extract common class libraries, such as some utility class methods. Our traditional practice is to write a utility class, populate the relevant tool methods into utility, and finally put the utility class into a global variable, so that utility methods can be called anywhere. If you use AngularJS's service, you create a utility service according to his rules, and then you can invoke methods in utility anywhere through dependency injection. There are three ways for Angular to create services: providers,factory,service,. You can see the difference between provider, factory and service in AngularJS

author: Xu Haifeng
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service is an encapsulation of the model layer, and the extraction of common class libraries is usually used to manage data and requests.

angular.
one is that injectable service, is decorated with @ Injectable, which uses the idea of dependency injection. You can inject other service, into component, such as passing values to each other as a bridge between two component, or as an application-level service, such as authentication, dirty check, and so on.
the other is non-injectable service, that is, it is not decorated with @ Injectable.
then its function is very simple, that is, it is an auxiliary class.

you can uniformly manage data requests in service