Angular 17+ : Blending Angular's Old and New Architectures with Standalone Components

One of the most significant changes in Angular 17 is the introduction of standalone components. These components can function independently without being declared in a module. This shift has simplified project structure and reduced boilerplate code.

A newly created Angular 17 projects might not include the traditional app.module.ts and app-routing.module.ts files by default. This change is primarily due to Angular's shift towards standalone components, a feature that was introduced in Angular 14 and has become more prominent in subsequent versions, including Angular 17.

Angular 17: A Shift Towards Implicit Modules

One of the notable changes in Angular 17 is the removal of the explicit app.module.ts file. This shift towards implicit modules offers several advantages:

1. Simplified Project Structure

• Fewer Files: By eliminating the explicit app.module.ts file, Angular 17 reduces the number of files in your project, making it more streamlined and easier to navigate.
• Reduced Complexity: Fewer files mean less complexity, making it easier for developers to understand and maintain their projects.

2. Improved Developer Experience

• Simplified Setup: The implicit module approach simplifies the initial setup process for new projects, as developers don't need to create and configure the app.module.ts file manually.
• Reduced Boilerplate: The removal of the explicit module reduces the amount of boilerplate code that developers need to write, allowing them to focus on building their application's core features.

3. Enhanced Flexibility

• Dynamic Module Creation: Angular 17's implicit modules provide greater flexibility in how modules are created and managed. Developers can dynamically create modules based on specific conditions or user interactions.
• Custom Bootstrapping: The implicit module approach allows for more customized bootstrapping strategies, enabling developers to tailor the application's startup process to their specific needs.

4. Improved Performance

• Optimized Bootstrapping: The implicit module approach can potentially lead to improved performance by optimizing the bootstrapping process and reducing the initial load time of the application.

5. Reduced Complexity

• The elimination of modules streamlines the project structure, making it easier to understand and maintain.

The removal of the explicit app.module.ts file in Angular 17 is a significant change that offers several benefits, including a simplified project structure, improved developer experience, enhanced flexibility, and potentially improved performance. By embracing this change, developers can create more efficient and maintainable Angular applications.

While Angular 17 doesn't explicitly include an app.module.ts file by default, it still uses the concept of modules behind the scenes.

Here's why:

1. Root Module: The Angular CLI automatically generates a root module, even if it's not explicitly defined in a separate file. This root module acts as the entry point for our application and is responsible for bootstrapping the application.
2. Implicit Creation: The root module is created implicitly based on the app.component.ts file. When we create a new Angular project, the CLI automatically generates the app.component.ts file, which is associated with the root module.
3. Behind the Scenes: While we don't see an explicit app.module.ts file, the root module's functionality is still present and active in our application.

Accessing the Root Module:

If we ever need to access or modify the root module, we can do so using the APP_INITIALIZER token or by injecting the ApplicationRef service.

In summary: While the Angular CLI doesn't generate an explicit app.module.ts file by default, it still uses the concept of modules to structure and bootstrap our application. The root module is implicitly created and serves as the entry point for our application.

Understanding the Shift to Standalone Components

1. Standalone Components:

• Definition: Standalone components allow you to build Angular applications without the need for NgModules (@NgModule). Each component can declare its dependencies directly.
• Benefits:

Simplified Structure: Reduces boilerplate by eliminating the need for module files.

Improved Tree Shaking: Potentially better performance due to more efficient bundling.

Easier Lazy Loading: Simplifies the setup for lazy-loaded modules.

2. Default Project Setup:

Angular CLI Defaults: Starting with Angular 14 and continuing into Angular 17, the Angular CLI provides options to create projects using standalone components. When you generate a new project with these defaults, it opts for standalone components, thereby omitting app.module.ts and app-routing.module.ts.

Modern Approach: This aligns with Angular's direction towards a more modular and flexible architecture.

Creating a Project with NgModules in Angular 17

If we prefer using NgModules and want the traditional app.module.ts and app-routing.module.ts files in your project, we can explicitly specify this when creating our project:

Using Angular CLI Flags:

ng new your-project-name --standalone=false        

Explanation: The --standalone=false flag tells the Angular CLI to generate the project using the traditional NgModule-based architecture.

Example:

ng new my-angular-app --standalone=false        

This command will generate a new Angular project named my-angular-app with app.module.ts and app-routing.module.ts included.

Migrating to Standalone Components

If you have an existing project using NgModules and want to migrate to standalone components, Angular provides a migration path. However, this process can be involved and requires careful planning. Here's a high-level overview:

1. Identify Components, Directives, and Pipes: Start by identifying which components can be converted to standalone.
2. Update Component Decorators: Add the standalone: true property to the @Component decorator.
3. Adjust Imports: Since standalone components manage their own imports, you'll need to adjust how dependencies are imported.
4. Remove NgModules: Gradually remove NgModules as components become standalone.

For detailed steps, refer to the Angular Standalone Components Guide.

Using Routing with Standalone Components

Even without app-routing.module.ts, you can still set up routing in a standalone-based Angular project:

1. Define Routes in main.ts or a Dedicated Routing File:

import { bootstrapApplication } from '@angular/platform-browser';
import { provideRouter, RouterModule } from '@angular/router';
import { AppComponent } from './app/app.component';
import { HomeComponent } from './app/home/home.component';
import { AboutComponent } from './app/about/about.component';

const routes = [
  { path: '', component: HomeComponent },
  { path: 'about', component: AboutComponent },
];

bootstrapApplication(AppComponent, {
  providers: [provideRouter(routes)],
});        

1. Benefits:

• Simplified Configuration: Routing can be configured without a separate routing module.
• Modularity: Each standalone component manages its own routing configuration if needed.

Angular 17 continues to support both traditional NgModule-based architecture and the newer standalone components approach. The Angular CLI's default behavior has shifted towards standalone components to leverage their benefits, which is why app.module.ts and app-routing.module.ts might not appear in newly created projects unless explicitly requested.

If we prefer the traditional structure, use the --standalone=false flag when generating a new project. Otherwise, embrace the standalone components approach for a more modern and streamlined Angular development experience.

we can absolutely use standalone components within a traditional Angular project (with NgModules). Angular is flexible enough to allow both approaches to coexist, so we can progressively introduce standalone components into our existing NgModule-based project. Here's how we can achieve that:

Steps to Add Standalone Components in a Traditional Angular Project

• Generate a Standalone Component: we can create a new standalone component using the Angular CLI with the --standalone flag. Even though our project is using NgModules, standalone components can still be added and used.

ng generate component standalone-component-name --standalone        

This will generate a component with the following structure:

• standalone: true in the @Component decorator.
• Direct dependencies like CommonModule or any other required modules are declared directly in the component.

import { Component } from '@angular/core';
import { CommonModule } from '@angular/common';

@Component({
  selector: 'app-standalone-component',
  standalone: true,
  imports: [CommonModule],
  templateUrl: './standalone-component.component.html',
  styleUrls: ['./standalone-component.component.scss']
})
export class StandaloneComponent { }        

• Use the Standalone Component in a Traditional NgModule: Even though the component is standalone, it can be used like any other component in our traditional NgModule-based Angular application.

Simply import the standalone component where you need it.

In your app.module.ts:

import { NgModule } from '@angular/core';
import { BrowserModule } from '@angular/platform-browser';
import { AppComponent } from './app.component';
import { StandaloneComponent } from './standalone-component/standalone-component.component';

@NgModule({
  declarations: [
    AppComponent,
    // You do not need to declare the standalone component here
  ],
  imports: [
    BrowserModule,
    StandaloneComponent, // Import standalone component directly
  ],
  providers: [],
  bootstrap: [AppComponent]
})
export class AppModule { }        

This works because standalone components are self-contained and do not need to be declared in an NgModule.

• Routing to a Standalone Component: If you want to route to a standalone component, you can do that without adding it to a module.

In app-routing.module.ts:

import { NgModule } from '@angular/core';
import { RouterModule, Routes } from '@angular/router';
import { StandaloneComponent } from './standalone-component/standalone-component.component';

const routes: Routes = [
  { path: 'standalone', component: StandaloneComponent },
  // other routes
];

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

• Using Standalone Components with Lazy Loading: Standalone components also support lazy loading. You can set them up in the routing configuration for lazy loading like so:

const routes: Routes = [
  { 
    path: 'standalone', 
    loadComponent: () => import('./standalone-component/standalone-component.component').then(m => m.StandaloneComponent) 
  },
];        

This lazy loads the standalone component when the user navigates to the standalone route.

Why Use Standalone Components in a Traditional NgModule Project?

• Progressive Migration: You can start migrating parts of your application to standalone components without refactoring everything.
• Modularity: Standalone components allow for more modular, reusable components that declare their own dependencies.
• Performance: Standalone components have better tree-shaking capabilities, potentially improving your application's performance.

We can easily create and use standalone components within a traditional Angular project (with NgModules). This approach lets us progressively adopt the standalone component model without refactoring the entire project. It also offers more flexibility for future migrations as Angular continues evolving toward a more modular structure.

Here’s an overview of the default features and project structure mechanism in Angular 17, which highlights how Angular's development has evolved:

1. Standalone Components (Optional)

• Default Structure: By default, Angular 17 emphasizes standalone components over NgModules. When creating a new project, the Angular CLI does not generate app.module.ts or app-routing.module.ts unless specified.
• Benefits:

Reduces the need for @NgModule, streamlining component management.

Allows components to manage their own dependencies directly via imports.

Facilitates better tree-shaking and lazy loading, enhancing performance.

• Opting for Traditional NgModules: To use the traditional NgModule-based structure, you can create a project with --standalone=false, which includes app.module.ts and follows the classic structure.

2. Project Structure with Standalone Components

When creating a project without the --standalone=false flag (i.e., the default structure in Angular 17), here’s what you get:

• main.ts: The main entry point of the application where the bootstrapApplication() function is used to initialize the root component (which is standalone).

import { bootstrapApplication } from '@angular/platform-browser';
import { AppComponent } from './app/app.component';

bootstrapApplication(AppComponent);        

• No app.module.ts: There’s no root NgModule generated by default, as the application bootstraps using standalone components.
• Routing Setup: Even without app-routing.module.ts, routing can be defined and managed directly using standalone components or loaded using provideRouter in the main.ts or another file.

import { provideRouter } from '@angular/router';
import { routes } from './app/app.routes';

bootstrapApplication(AppComponent, {
  providers: [provideRouter(routes)],
});        

3. Optional Traditional Project Structure

If you create a project with --standalone=false, Angular will generate the traditional structure:

• app.module.ts:

The root NgModule acts as the main module for bootstrapping the app.

This module imports all dependencies and declarations (components, directives, pipes) as in previous Angular versions.

• app-routing.module.ts:

If routing is required, this file manages the routing configuration using RouterModule.forRoot().

This traditional structure is still fully supported and can work alongside the newer standalone component approach, enabling a gradual migration path.

4. Other Key Features in Angular 17

• Module Federation for Micro Frontends: Angular 17 continues to support micro frontend architecture using native Module Federation, allowing teams to split their applications into independently deployable modules.
• Improved Dependency Injection: Angular 17 enhances dependency injection mechanisms for better performance and flexibility.
• Optimized Rendering: Angular’s Ivy rendering engine has seen further improvements in Angular 17, with better performance optimizations, reducing overhead for complex components.
• Directives as Standalone: Directives and pipes can also be made standalone, further reducing the reliance on NgModules.

5. Project Structure Overview in Angular 17

Whether using standalone components or the traditional module-based architecture, Angular 17 keeps the general structure clean and modular. Here’s an outline:

• src/app/:

app.component.ts: The root component, whether standalone or declared in a module.

Standalone or NgModule Components: Each feature or component may either be a standalone component or follow the traditional NgModule structure.

• main.ts: The entry point of the application, either bootstrapping with NgModules or using bootstrapApplication() for standalone components.
• app.routes.ts (optional): Manages routing for standalone components, or you can keep the traditional routing setup in app-routing.module.ts.

Angular 17 offers flexibility by allowing you to choose between:

• The standalone components approach for cleaner, module-free architecture and better tree-shaking.
• The traditional NgModule approach for maintaining compatibility with older projects.

We can use standalone components in both new and existing Angular projects, allowing for a smooth transition and enabling modern Angular features while maintaining familiarity with the older project structure.

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