How can handle have multiple lazy-loaded modules with a large number of Angular components

 If you have multiple lazy-loaded modules with a large number of components, there are several strategies and best practices you can adopt to ensure that your Angular application remains performant, maintainable, and scalable.

Here are some tips for handling large applications with multiple lazy-loaded modules:

1. Split Large Modules into Smaller Modules

Rather than having one large lazy-loaded module with hundreds of components, you can split your large modules into smaller feature modules. This will help reduce the initial load time and make it easier to manage and maintain your application.

For example, instead of having a single AdminModule with everything in it, you can break it down like this:

• AdminModule
  • AdminDashboardModule
  • UserManagementModule
  • ReportsModule
  • SettingsModule

This way, each part of the admin section is split into separate lazy-loaded modules.

typescript

// Admin Routing Example
{
  path: 'admin', 
  loadChildren: () => import('./admin/admin.module')
.then(m => m.AdminModule)
}

{
  path: 'admin/dashboard', 
  loadChildren: () => 
import('./admin-dashboard/admin-dashboard.module').then(m => 
m.AdminDashboardModule)
}

This allows each part of the app to be loaded separately when needed, keeping the initial payload small.

2. Tree Shakable Modules

Angular automatically supports tree shaking, which removes unused code from the final bundle during production builds. To maximize tree shaking, ensure that your modules and components are well-organized, and don't export things you don't need.

• Avoid exporting unnecessary services or components from modules that are not supposed to be used outside.
• Keep the modules focused and encapsulated, and avoid making them too "public."

typescript

// Avoid exporting unneeded services
@NgModule({
  providers: [SomeService] 
// Avoid exporting this if it is 
//meant to be used internally
})
export class SomeModule { }

3. Use PreloadingStrategy for Faster Navigation

By default, lazy-loaded modules are only loaded when a user navigates to them. However, you can improve performance by using a preloading strategy to load modules in the background after the initial app load. This can reduce waiting times when users navigate to these modules.

Angular has a default preloading strategy (PreloadAllModules), but you can create a custom preloading strategy if you only want to preload specific modules.

typescript

import { NgModule } from '@angular/core';
import { PreloadAllModules, RouterModule, Routes } 
from '@angular/router';

const routes: Routes = [
  {
    path: 'user', loadChildren: () => 
import('./user/user.module').then(m => m.UserModule)
  },
  {
    path: 'admin', loadChildren: () => 
import('./admin/admin.module').then(m => m.AdminModule)
  },
];

@NgModule({
  imports: [RouterModule.forRoot(routes,
 { preloadingStrategy: PreloadAllModules })],
  exports: [RouterModule]
})
export class AppRoutingModule { }

By using preloading, modules are fetched in the background after the initial load, which can improve performance when users navigate between different sections of the app.

4. Optimizing Lazy Loading with loadChildren

When working with multiple lazy-loaded modules, be mindful of how you organize your routing to avoid unnecessary loading. If a module isn't accessed frequently, you can make its loading conditional or split it further into more granular routes.

• Split routing: Instead of loading all components at once in one lazy-loaded module, consider splitting them based on use case (e.g., based on user roles or other conditions).

• Use loadChildren with sub-modules: For large feature modules, consider adding lazy loading for sub-modules. For instance, an AdminModule could load AdminDashboardModule and AdminUserModule only when the user navigates to those parts.

5. Code Splitting and Dynamic Imports

Code splitting in Angular allows you to load different bundles (files) of code only when they are required, avoiding large initial bundles. This is mostly handled automatically when using lazy loading (loadChildren). You can also take advantage of dynamic imports in Angular for other use cases, such as loading specific services, components, or libraries only when necessary.

Example of dynamic import for an optional component:

typescript

import { Component, ViewContainerRef, ComponentFactoryResolver } 
from '@angular/core';

@Component({
  selector: 'app-dynamic',
  template: `<button
 (click)="loadComponent()">Load Component</button>`
})
export class DynamicComponent {
  constructor(private viewContainerRef: ViewContainerRef,
              private cfr: ComponentFactoryResolver) {}

  loadComponent() {
    import('./optional/optional.component').then(({ OptionalComponent }) => {
      const factory = this.cfr.resolveComponentFactory(OptionalComponent);
      this.viewContainerRef.createComponent(factory);
    });
  }
}

6. Use Angular's Built-in Caching for Lazy Loaded Modules

Angular has a built-in module caching mechanism that prevents reloading the module if it has already been loaded. However, you can still optimize your app by using local storage or session storage to cache frequently used data or state within the lazy-loaded modules.

7. AOT Compilation and Production Builds

Always use Ahead-of-Time (AOT) compilation in production. This reduces the size of the Angular app, as it compiles the application during the build process rather than at runtime, resulting in smaller and faster applications.

bash

ng build --prod

This step ensures that your app will be highly optimized for production.

8. Track Lazy Loading Performance

You can use Angular's built-in performance tools or third-party libraries like Webpack Bundle Analyzer to see which parts of your app are taking too long to load. You can then optimize those areas by splitting them further or preloading them.

9. Preloading Strategy per Module (Optional)

Instead of preloading all modules, you can implement a custom preloading strategy that preloads only specific modules based on certain conditions (e.g., if a user is authenticated, preload the admin module).

typescript

import { Injectable } from '@angular/core';
import { PreloadingStrategy, Route } from '@angular/router';
import { Observable, of } from 'rxjs';

@Injectable({
  providedIn: 'root'
})
export class CustomPreloadingStrategy implements PreloadingStrategy {
  preload(route: Route, load: Function): Observable<any> {
    return route.data && route.data['preload'] ? load() : of(null);
  }
}

Then, configure it in the router:

typescript

const routes: Routes = [
  {
    path: 'user', loadChildren: () => 
import('./user/user.module').then(m => m.UserModule),
    data: { preload: true }
  },
  {
    path: 'admin', loadChildren: () =>
 import('./admin/admin.module').then(m => m.AdminModule),
    data: { preload: false }
  },
];

@NgModule({
  imports: [RouterModule.forRoot(routes, 
{ preloadingStrategy: CustomPreloadingStrategy })],
  exports: [RouterModule]
})
export class AppRoutingModule { }

Summary:

For large apps with many lazy-loaded modules:

1. Split your modules: Break up large modules into smaller feature-based modules.
2. Use tree shaking: Ensure your code is tree-shakable by avoiding unnecessary exports.
3. Implement preloading strategies: Preload some modules or submodules to improve the user experience.
4. Lazy load only what's necessary: Avoid loading too many modules or components at once.
5. Optimize builds: Use AOT compilation and production builds for smaller and faster apps.
6. Use dynamic imports: Dynamically load components or services as needed.