I am trying to understand Angular (sometimes called Angular2+), then I came across @Module
:
Imports
Declarations
Providers
Following Angular Quick Start
I am trying to understand Angular (sometimes called Angular2+), then I came across @Module
:
Imports
Declarations
Providers
Following Angular Quick Start
Angular Concepts
imports
makes the exported declarations of other modules available in the current moduledeclarations
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).
For more details about modules see also https://angular.io/docs/ts/latest/guide/ngmodule.html
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.
entryComponents
registers components for offline compilation so that they can be used with ViewContainerRef.createComponent()
. Components used in router configurations are added implicitly.
TypeScript (ES2015) imports
import ... from 'foo/bar'
(which may resolve to an index.ts
) are for TypeScript imports. You need these whenever you use an identifier in a typescript file that is declared in another typescript file.
Angular's @NgModule()
imports
and TypeScript import
are entirely different concepts.
See also jDriven - TypeScript and ES6 import syntax
Most of them are actually plain ECMAScript 2015 (ES6) module syntax that TypeScript uses as well.
imports
are used to import supporting modules like FormsModule, RouterModule, CommonModule, or any other custom-made feature module.
declarations
are used to declare components, directives, pipes that belong to the current module. Everyone inside declarations knows each other. For example, if we have a component, say UsernameComponent, which displays a list of the usernames and we also have a pipe, say toupperPipe, which transforms a string to an uppercase letter string. Now If we want to show usernames in uppercase letters in our UsernameComponent then we can use the toupperPipe which we had created before but the question is how UsernameComponent knows that the toupperPipe exists and how it can access and use that. Here come the declarations, we can declare UsernameComponent and toupperPipe.
Providers
are used for injecting the services required by components, directives, pipes in the module.
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 { }
Adding a quick cheat sheet that may help after the long break with Angular:
Example:
declarations: [AppComponent]
What can we inject here? Components, pipes, directives
Example:
imports: [BrowserModule, AppRoutingModule]
What can we inject here? other modules
Example:
providers: [UserService]
What can we inject here? services
Example:
bootstrap: [AppComponent]
What can we inject here? the main component that will be generated by this module (top parent node for a component tree)
Example:
entryComponents: [PopupComponent]
What can we inject here? dynamically generated components (for instance by using ViewContainerRef.createComponent())
Example:
export: [TextDirective, PopupComponent, BrowserModule]
What can we inject here? components, directives, modules or pipes that we would like to have access to them in another module (after importing this module)
@NgModule
constructs:import { x } from 'y';
: This is standard typescript syntax (ES2015/ES6
module syntax) for importing code from other files. This is not Angular specific. Also this is technically not part of the module, it is just necessary to get the needed code within scope of this file.imports: [FormsModule]
: You import other modules in here. For example we import FormsModule
in the example below. Now we can use the functionality which the FormsModule has to offer throughout this module.declarations: [OnlineHeaderComponent, ReCaptcha2Directive]
: You put your components, directives, and pipes here. Once declared here you now can use them throughout the whole module. For example we can now use the OnlineHeaderComponent
in the AppComponent
view (html file). Angular knows where to find this OnlineHeaderComponent
because it is declared in the @NgModule
.providers: [RegisterService]
: Here our services of this specific module are defined. You can use the services in your components by injecting with dependency injection.// Angular
import { BrowserModule } from '@angular/platform-browser';
import { NgModule } from '@angular/core';
import { FormsModule } from '@angular/forms';
// Components
import { AppComponent } from './app.component';
import { OfflineHeaderComponent } from './offline/offline-header/offline-header.component';
import { OnlineHeaderComponent } from './online/online-header/online-header.component';
// Services
import { RegisterService } from './services/register.service';
// Directives
import { ReCaptcha2Directive } from './directives/re-captcha2.directive';
@NgModule({
declarations: [
OfflineHeaderComponent,,
OnlineHeaderComponent,
ReCaptcha2Directive,
AppComponent
],
imports: [
BrowserModule,
FormsModule,
],
providers: [
RegisterService,
],
entryComponents: [
ChangePasswordComponent,
TestamentComponent,
FriendsListComponent,
TravelConfirmComponent
],
bootstrap: [AppComponent]
})
export class AppModule { }