What is the difference between declarations, providers, and import in NgModule?

Angular Concepts

• imports makes the exported declarations of other modules available in the current module
• declarations are to make directives (including components and pipes) from the current module available to other directives in the current module. Selectors of directives, components or pipes are only matched against the HTML if they are declared or imported.
• providers are to make services and values known to DI (dependency injection). They are added to the root scope and they are injected to other services or directives that have them as dependency.

A special case for providers are lazy loaded modules that get their own child injector. providers of a lazy loaded module are only provided to this lazy loaded module by default (not the whole application as it is with other modules).

1. exports makes the components, directives, and pipes available in modules that add this module to imports. exports can also be used to re-export modules such as CommonModule and FormsModule, which is often done in shared modules
2. entryComponents registers components for offline compilation so that they can be used with ViewContainerRef.createComponent(). Components used in router configurations are added implicitly.

Angular's @NgModule() imports and TypeScript import are entirely different concepts.


Components are declared, Modules are imported, and Services are provided. An example I'm working with:

import { BrowserModule } from '@angular/platform-browser';
import { NgModule } from '@angular/core';


import { AppComponent } from './app.component';
import {FormsModule} from '@angular/forms';
import { UserComponent } from './components/user/user.component';
import { StateService } from './services/state.service';   

@NgModule({
  declarations: [
    AppComponent,
    UserComponent
  ],
  imports: [
    BrowserModule,
    FormsModule
  ],
  providers: [ StateService ],
  bootstrap: [ AppComponent ]
})
export class AppModule { }