NgModules

Prerequisites

A basic understanding of the following concepts:

• Bootstrapping.
• JavaScript Modules vs. NgModules.

NgModules configure the injector and the compiler and help organize related things together.

An NgModule is a class marked by the @NgModule decorator. @NgModule takes a metadata object that describes how to compile a component's template and how to create an injector at runtime. It identifies the module's own components, directives, and pipes, making some of them public, through the exports property, so that external components can use them. @NgModule can also add service providers to the application dependency injectors.

For an example app showcasing all the techniques that NgModules related pages cover, see the live example. For explanations on the individual techniques, visit the relevant NgModule pages under the NgModules section.

Angular modularity

Modules are a great way to organize an application and extend it with capabilities from external libraries.

Angular libraries are NgModules, such as FormsModule, HttpClientModule, and RouterModule. Many third-party libraries are available as NgModules such as Material Design, Ionic, and AngularFire2.

NgModules consolidate components, directives, and pipes into cohesive blocks of functionality, each focused on a feature area, application business domain, workflow, or common collection of utilities.

Modules can also add services to the application. Such services might be internally developed, like something you'd develop yourself or come from outside sources, such as the Angular router and HTTP client.

Modules can be loaded eagerly when the application starts or lazy loaded asynchronously by the router.

NgModule metadata does the following:

• Declares which components, directives, and pipes belong to the module.
• Makes some of those components, directives, and pipes public so that other module's component templates can use them.
• Imports other modules with the components, directives, and pipes that components in the current module need.
• Provides services that the other application components can use.

Every Angular app has at least one module, the root module. You bootstrap that module to launch the application.

The root module is all you need in a simple application with a few components. As the app grows, you refactor the root module into feature modules that represent collections of related functionality. You then import these modules into the root module.

The basic NgModule

The CLI generates the following basic app module when creating a new app.

// imports
import { BrowserModule } from '@angular/platform-browser';
import { NgModule } from '@angular/core';
import { FormsModule } from '@angular/forms';
import { HttpClientModule } from '@angular/common/http';

import { AppComponent } from './app.component';
import { ItemDirective } from './item.directive';


// @NgModule decorator with its metadata
@NgModule({
  declarations: [
    AppComponent,
    ItemDirective
  ],
  imports: [
    BrowserModule,
    FormsModule,
    HttpClientModule
  ],
  providers: [],
  bootstrap: [AppComponent]
})
export class AppModule { }

At the top are the import statements. The next section is where you configure the @NgModule by stating what components and directives belong to it (declarations) as well as which other modules it uses (imports). This page builds on Bootstrapping, which covers the structure of an NgModule in detail. If you need more information on the structure of an @NgModule, be sure to read Bootstrapping.

More on NgModules

You may also be interested in the following:

• Feature Modules.
• Entry Components.
• Providers.
• Types of NgModules.