LazyLoadingModules

Purpose

The purpose of this repository is to present a POC of a plugin system, and provide a way for these modules to expose API in a unified way. PluginModules should be lazy-loadable. When lazy-loaded, they should be conditinally loaded (like canLoad with lazy loaded routes).

Why not use the routing mechanism?

This is a POC which will hopefully, after refactoring and improving, be used in a certain app.
This app does not rely on routing, and basically has two routes: /login and /app.
The /app contains a big application, with a map, and a lot of map elements and floating forms.
Under certain curcuimstences, we don't want to load all feature modules -

• Different environments
• A/B Testing
• Etc

And so, I want to provide a way for modules to expose some api, that will be available to the app, if and once loaded.

Structure

The main library is in /projects/plugin-modules.
It contains the entire plugin modules API, and exposes services which are needed to interact with, an plug into, the plugin module system.

The example plugin system is in /projects/forms-registry.
The purpose of the library is to save and expose a registry of components with certain attributes (e.g: each component has a category, code, etc.).

Each feature module can expose such components by using the forms-registry library.

The Example Application

The app component shows a simple menu with all the components from the registry. Clicking on a component name loads the component below the menu.

Plugin System

Each plugin system can expose instances of the PluginProcessor interface.

// From library
export interface PluginProcessor {
  process(moduleRef: NgModuleRef<any>): void | Promise<void> | Observable<void>;
}

// Userland
export class MyProcessor implements PluginProcessor { ... }

NgModule({
  providers: [
    providePluginProcessor(MyProcessor),
  ],
})
class MyPluginSystemModule { ... }

Plugin systems can save whatever data they want on modules via providers.

When a feature module is loaded and boostrapped, it is ran through the PluginProcessorsService which saves all PluginProcessors and activates them.

When the plugin system processor is activated, this is where you can collect the data saved on the module, and act accordingly.

The Example Plugin System: Forms Registry

The library exposes the FormsRegistryService which is the main public API for the plugin system:

@Injectable()
export class FormsRegistry {
  formEntries$(): Observable<FormEntry[]>;

  add<T = any>(
    formEntry: FormEntry<T>,
    componentFactory: ComponentFactory<T>
  ): void;

  resolveComponentFactory<T>(component: Type<T>): ComponentFactory<T> | null;
}

The plugin system registers the PluginProcessor via a forRoot import:

@NgModule({
  imports: [
    PluginsModule.forRoot([
      {
        loadChildren: () =>
          import("./feature1/feature1.module").then(m => m.Feature1Module),
        name: "feature1" // name provided for diagnostics
      }
    ]),
    FormsRegistryModule.forRoot()
  ]
})
export class AppModule {}

Feature Modules expose forms to the registry via a forFeature import:

@NgModule({
  declarations: [Feature1FormComponent],
  imports: [
    CommonModule,
    FormsRegistryModule.forFeature([
      {
        category: "Category 1",
        component: Feature1FormComponent,
        name: "Feature1FormComponent"
      }
    ]), // expose api
    PluginsModule.forFeature() // register as module that exposes api via plugins
  ],
})
export class Feature1Module {}

When the module is loaded, the FormsRegistryProcessor collects the forms provided in the feature module, and loads them into the registry with FormRegistryService#add.

ANGULAR CLI GENERATED STUFF

This project was generated with Angular CLI version 8.2.2.

Development server

Run ng serve for a dev server. Navigate to http://localhost:4200/. The app will automatically reload if you change any of the source files.

Code scaffolding

Run ng generate component component-name to generate a new component. You can also use ng generate directive|pipe|service|class|guard|interface|enum|module.

Build

Run ng build to build the project. The build artifacts will be stored in the dist/ directory. Use the --prod flag for a production build.

Running unit tests

Run ng test to execute the unit tests via Karma.

Running end-to-end tests

Run ng e2e to execute the end-to-end tests via Protractor.

Further help

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