How to Pass Backend-Rendered Parameters to Angular 2 Bootstrap for Setting HTTP Headers?

Angular2 Bootstrap Parameters from Backend using Dependency Injection

Problem:

In Angular2, how can parameters rendered on the backend be passed to the bootstrap method to set HTTP headers for all requests using BaseRequestOptions?

Solution:

Utilizing Angular's dependency injection, parameters can be passed directly to the bootstrap function:

var headers = ... // retrieve headers from backend

bootstrap(AppComponent, [{provide: 'headers', useValue: headers})]);

To inject the headers into components or services, use the @Inject() decorator:

class SomeComponentOrService {
   constructor(@Inject('headers') private headers) {}
}

Alternatively, a custom request options class can be created and injected directly:

class MyRequestOptions extends BaseRequestOptions {
  constructor (private headers) {
    super();
  }
} 

var values = ... // retrieve headers from backend
var headers = new MyRequestOptions(values);

bootstrap(AppComponent, [{provide: BaseRequestOptions, useValue: headers})]);

Additional Approaches:

• APP_INITIALIZER: Initializes services with data from the backend before initializing the application. This is useful for setting header values.
• Constructor Injection: The Angular 2 constructor can be used for initialization instead of the bootstrap method.
• AoT (Ahead-of-Time Compilation): Some modifications are required to work with AoT, such as moving the factory closure out of the provider.
• Injector: If a cyclic dependency occurs (e.g., injecting the router), the Injector can be used to retrieve the dependency instead of direct injection.

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