arunpraba/angular-services

Services and Dependency injection⚡️

Services and Dependency injection

Few Important concents in angular Services Angular Services and Dependency injection

Services

Services are the class. which contains common functions, repetative Logics

Dependency Injection

Its a Mechanism to connect components to Service

useClass

Its a way to provide service to Module. It will create the new Instance

providers: [ { provide: PeopleService, useClass: PeopleService } ]

useExisting

Its a way to update old service wIth newService in Module. It will overwrIte old service

providers: [ InventorsService, { provide: PeopleService, useExisting: InventorsService } ]

useValue

Its a way to pass the object as service in Module.

const simpleEmployee = { getPeople() { return new EmployeeService().getPeople(); } };

providers: [ { provide: EmployeeService, useValue: simpleEmployee }, ]

useFactory

Its a way to pass the value to the service in Module.

const value = new EmployeeService(); const simpleReturn = () => { return value.getPeople(); };

providers: [ { provide: ManService, useFactory: simpleReturn } ]

@SkipSelf()

It will skip dependency check in component level

constructor( @SkipSelf() private inventorService:InventorService) { this.inventor = this.inventorService.getPeople() }

@Host(),

It will check dependency in component level

constructor( @Host() private inventorService:InventorService) { this.inventor = this.inventorService.getPeople() }

@Optional()

It will check dependency, if not available then It will provide null value

constructor( @Optional() private inventorService:InventorService) { this.inventor = this.inventorService.getPeople() }