Can I set CUSTOM_ELEMENTS_SCHEMA globally in Angular 17 without an application module?

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31-08-2024

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Setting CUSTOM_ELEMENTS_SCHEMA Globally in Angular 17 Without an Application Module

Migrating to Angular 17 and removing the app.module.ts file can be a great way to streamline your project, but it can also present challenges when you're used to the traditional approach of setting global configurations. One such challenge is applying the CUSTOM_ELEMENTS_SCHEMA globally to handle custom web components without needing to repeat it in every component.

The Problem:

You want to avoid adding schemas: [CUSTOM_ELEMENTS_SCHEMA] to each component definition to handle custom web components, especially if you're using them extensively throughout your application. This repetition can make your code less maintainable.

Solution:

While directly setting CUSTOM_ELEMENTS_SCHEMA in the appConfig object doesn't work, there's a simple solution:

1. Create a ComponentFactoryResolver Provider:

   import { ComponentFactoryResolver, Injector, Provider, Type } from '@angular/core';
   import { CUSTOM_ELEMENTS_SCHEMA } from '@angular/core';
   
   export const customElementsResolverProvider: Provider = {
     provide: ComponentFactoryResolver,
     useFactory: (injector: Injector) => {
       const resolver = injector.get(ComponentFactoryResolver);
       return {
         resolveComponentFactory: <T>(component: Type<T>): any => {
           const factory = resolver.resolveComponentFactory(component);
           factory.schema = [CUSTOM_ELEMENTS_SCHEMA];
           return factory;
         },
       };
     },
     deps: [Injector],
   };
   

2. Add the Provider to your app.config.ts:

   import { ApplicationConfig, importProvidersFrom } from '@angular/core';
   import { provideRouter } from '@angular/router';
   import { routes } from './app.routes';
   import { provideHttpClient, withInterceptors } from '@angular/common/http';
   import { CookieModule } from 'ngx-cookie';
   import { customElementsResolverProvider } from './custom-elements-resolver';
   
   export const appConfig: ApplicationConfig = {
     providers: [
       provideRouter(routes),
       provideHttpClient(),
       importProvidersFrom(CookieModule.withOptions()),
       customElementsResolverProvider, // Add this line
     ],
   };
   

Explanation:

• The customElementsResolverProvider creates a custom ComponentFactoryResolver that automatically applies CUSTOM_ELEMENTS_SCHEMA to all component factories.
• This custom resolver intercepts the default ComponentFactoryResolver and modifies its behavior. When a component factory is requested, it adds CUSTOM_ELEMENTS_SCHEMA to the factory's schema.

Benefits:

• Global Application: You no longer need to add schemas: [CUSTOM_ELEMENTS_SCHEMA] to each component, saving you time and improving code readability.
• No app.module.ts: This solution is ideal for projects without an app.module.ts file.
• Clean and Maintainable: Your code remains organized, with the schema configuration managed centrally.

Important Notes:

• Angular Version: This solution works with Angular 17 and later versions.
• Error Handling: It's important to handle potential errors related to resolving component factories. You can add appropriate error handling within the useFactory function.

Example:

Let's say you're using a custom web component named my-custom-element:

<my-custom-element></my-custom-element>

Thanks to the global CUSTOM_ELEMENTS_SCHEMA setup, Angular will successfully recognize and render this custom web component in your application without any additional configuration.

Attribution:

This solution is a combination of insights and techniques found on Stack Overflow. Special thanks to:

• @sandeepsingh: https://stackoverflow.com/a/74002455/11933679 for the initial idea and code structure.

By applying this solution, you can effectively handle custom web components in your Angular 17 project without needing an app.module.ts file, keeping your code clean and your application functioning seamlessly.