Why can abp.service.app in JS match services in the ABP framework

[hehetiger]

Generally, in JS, var _userService=abp. services. app. user; Define the GetUsers method in UserAppService, and in JavaScript, this method can be called by using _userService. getUser(). So how does the ABP framework find 'UserAppService' through 'abp. services. app. user', and where is the corresponding method implemented? I want to see how the underlying code implements this function。